include/swift/AST/Expr.h

//===--- Expr.h - Swift Language Expression ASTs ----------------*- C++ -*-===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2018 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
// This file defines the Expr class and subclasses.
//
//===----------------------------------------------------------------------===//

#ifndef SWIFT_AST_EXPR_H
#define SWIFT_AST_EXPR_H

#include "swift/AST/CaptureInfo.h"
#include "swift/AST/ConcreteDeclRef.h"
#include "swift/AST/DeclContext.h"
#include "swift/AST/DeclNameLoc.h"
#include "swift/AST/FunctionRefKind.h"
#include "swift/AST/ProtocolConformanceRef.h"
#include "swift/AST/TrailingCallArguments.h"
#include "swift/AST/TypeAlignments.h"
#include "swift/AST/Availability.h"
#include "swift/Basic/Debug.h"
#include "swift/Basic/InlineBitfield.h"
#include "llvm/Support/TrailingObjects.h"
#include <utility>

namespace llvm {
  struct fltSemantics;
}

namespace swift {
  enum class AccessKind : unsigned char;
  class ArchetypeType;
  class ASTContext;
  class AvailabilitySpec;
  class IdentTypeRepr;
  class Type;
  class TypeRepr;
  class ValueDecl;
  class Decl;
  class DeclRefExpr;
  class OpenedArchetypeType;
  class ParamDecl;
  class Pattern;
  class SubscriptDecl;
  class Stmt;
  class BraceStmt;
  class ASTWalker;
  class Initializer;
  class VarDecl;
  class OpaqueValueExpr;
  class FuncDecl;
  class ConstructorDecl;
  class TypeDecl;
  class PatternBindingDecl;
  class ParameterList;
  class EnumElementDecl;
  class CallExpr;
  class KeyPathExpr;
  class CaptureListExpr;

struct TrailingClosure {
  Identifier Label;
  SourceLoc LabelLoc;
  Expr *ClosureExpr;

  TrailingClosure(Expr *closure)
      : TrailingClosure(Identifier(), SourceLoc(), closure) {}

  TrailingClosure(Identifier label, SourceLoc labelLoc, Expr *closure)
      : Label(label), LabelLoc(labelLoc), ClosureExpr(closure) {}
};

enum class ExprKind : uint8_t {
#define EXPR(Id, Parent) Id,
#define LAST_EXPR(Id) Last_Expr = Id,
#define EXPR_RANGE(Id, FirstId, LastId) \
  First_##Id##Expr = FirstId, Last_##Id##Expr = LastId,
#include "swift/AST/ExprNodes.def"
};
enum : unsigned { NumExprKindBits =
  countBitsUsed(static_cast<unsigned>(ExprKind::Last_Expr)) };
  
/// Discriminates certain kinds of checked cast that have specialized diagnostic
/// and/or code generation peephole behavior.
///
/// This enumeration should not have any semantic effect on the behavior of a
/// well-typed program, since the runtime can perform all casts that are
/// statically accepted.
enum class CheckedCastKind : unsigned {
  /// The kind has not been determined yet.
  Unresolved,

  /// Valid resolved kinds start here.
  First_Resolved,

  /// The requested cast is an implicit conversion, so this is a coercion.
  Coercion = First_Resolved,
  /// A checked cast with no known specific behavior.
  ValueCast,
  // A downcast from an array type to another array type.
  ArrayDowncast,
  // A downcast from a dictionary type to another dictionary type.
  DictionaryDowncast,
  // A downcast from a set type to another set type.
  SetDowncast,
  /// A bridging conversion that always succeeds.
  BridgingCoercion,

  Last_CheckedCastKind = BridgingCoercion,
};

/// What are the high-level semantics of this access?
enum class AccessSemantics : uint8_t {
  /// On a storage reference, this is a direct access to the underlying
  /// physical storage, bypassing any observers.  The declaration must be 
  /// a variable with storage.
  ///
  /// On a function reference, this is a non-polymorphic access to a
  /// particular implementation.
  DirectToStorage,

  /// On a storage reference, this is a direct access to the concrete
  /// implementation of this storage, bypassing any possibility of override.
  DirectToImplementation,

  /// This is an ordinary access to a declaration, using whatever
  /// polymorphism is expected.
  Ordinary,
};

/// Expr - Base class for all expressions in swift.
class alignas(8) Expr {
  Expr(const Expr&) = delete;
  void operator=(const Expr&) = delete;

protected:
  union { uint64_t OpaqueBits;

  SWIFT_INLINE_BITFIELD_BASE(Expr, bitmax(NumExprKindBits,8)+1,
    /// The subclass of Expr that this is.
    Kind : bitmax(NumExprKindBits,8),
    /// Whether the Expr represents something directly written in source or
    /// it was implicitly generated by the type-checker.
    Implicit : 1
  );

  SWIFT_INLINE_BITFIELD_FULL(CollectionExpr, Expr, 64-NumExprBits,
    /// True if the type of this collection expr was inferred by the collection
    /// fallback type, like [Any].
    IsTypeDefaulted : 1,
    /// Number of comma source locations.
    NumCommas : 32 - 1 - NumExprBits,
    /// Number of entries in the collection. If this is a DictionaryExpr,
    /// each entry is a Tuple with the key and value pair.
    NumSubExprs : 32
  );

  SWIFT_INLINE_BITFIELD_EMPTY(LiteralExpr, Expr);
  SWIFT_INLINE_BITFIELD_EMPTY(IdentityExpr, Expr);
  SWIFT_INLINE_BITFIELD(LookupExpr, Expr, 1,
    IsSuper : 1
  );
  SWIFT_INLINE_BITFIELD_EMPTY(DynamicLookupExpr, LookupExpr);

  SWIFT_INLINE_BITFIELD(ParenExpr, IdentityExpr, 1,
    /// Whether we're wrapping a trailing closure expression.
    HasTrailingClosure : 1
  );

  SWIFT_INLINE_BITFIELD(NumberLiteralExpr, LiteralExpr, 1+1,
    IsNegative : 1,
    IsExplicitConversion : 1
  );

  SWIFT_INLINE_BITFIELD(StringLiteralExpr, LiteralExpr, 3+1+1,
    Encoding : 3,
    IsSingleUnicodeScalar : 1,
    IsSingleExtendedGraphemeCluster : 1
  );

  SWIFT_INLINE_BITFIELD_FULL(InterpolatedStringLiteralExpr, LiteralExpr, 32+20,
    : NumPadBits,
    InterpolationCount : 20,
    LiteralCapacity : 32
  );

  SWIFT_INLINE_BITFIELD(DeclRefExpr, Expr, 2+2,
    Semantics : 2, // an AccessSemantics
    FunctionRefKind : 2
  );

  SWIFT_INLINE_BITFIELD(UnresolvedDeclRefExpr, Expr, 2+2,
    DeclRefKind : 2,
    FunctionRefKind : 2
  );

  SWIFT_INLINE_BITFIELD(MemberRefExpr, LookupExpr, 2,
    Semantics : 2 // an AccessSemantics
  );

  SWIFT_INLINE_BITFIELD_FULL(TupleElementExpr, Expr, 32,
    : NumPadBits,
    FieldNo : 32
  );

  SWIFT_INLINE_BITFIELD_FULL(TupleExpr, Expr, 1+1+32,
    /// Whether this tuple has any labels.
    HasElementNames : 1,

    /// Whether this tuple has label locations.
    HasElementNameLocations : 1,

    : NumPadBits,
    NumElements : 32
  );

  SWIFT_INLINE_BITFIELD(UnresolvedDotExpr, Expr, 2,
    FunctionRefKind : 2
  );

  SWIFT_INLINE_BITFIELD_FULL(SubscriptExpr, LookupExpr, 2+1+1+16,
    Semantics : 2, // an AccessSemantics
    /// Whether the SubscriptExpr also has source locations for the argument
    /// label.
    HasArgLabelLocs : 1,
    /// Whether the last argument is a trailing closure.
    HasTrailingClosure : 1,
    : NumPadBits,
    /// # of argument labels stored after the SubscriptExpr.
    NumArgLabels : 16
  );

  SWIFT_INLINE_BITFIELD_FULL(DynamicSubscriptExpr, DynamicLookupExpr, 1+1+16,
    /// Whether the DynamicSubscriptExpr also has source locations for the
    /// argument label.
    HasArgLabelLocs : 1,
    /// Whether the last argument is a trailing closure.
    HasTrailingClosure : 1,
    : NumPadBits,
    /// # of argument labels stored after the DynamicSubscriptExpr.
    NumArgLabels : 16
  );

  SWIFT_INLINE_BITFIELD_FULL(UnresolvedMemberExpr, Expr, 2,
    FunctionRefKind : 2
  );

  SWIFT_INLINE_BITFIELD(OverloadSetRefExpr, Expr, 2,
    FunctionRefKind : 2
  );

  SWIFT_INLINE_BITFIELD(BooleanLiteralExpr, LiteralExpr, 1,
    Value : 1
  );

  SWIFT_INLINE_BITFIELD(MagicIdentifierLiteralExpr, LiteralExpr, 3+1,
    Kind : 3,
    StringEncoding : 1
  );

  SWIFT_INLINE_BITFIELD_FULL(ObjectLiteralExpr, LiteralExpr, 3+1+1+16,
    LitKind : 3,
    /// Whether the ObjectLiteralExpr also has source locations for the argument
    /// label.
    HasArgLabelLocs : 1,
    /// Whether the last argument is a trailing closure.
    HasTrailingClosure : 1,
    : NumPadBits,
    /// # of argument labels stored after the ObjectLiteralExpr.
    NumArgLabels : 16
  );

  SWIFT_INLINE_BITFIELD(AbstractClosureExpr, Expr, (16-NumExprBits)+16,
    : 16 - NumExprBits, // Align and leave room for subclasses
    Discriminator : 16
  );

  SWIFT_INLINE_BITFIELD(AutoClosureExpr, AbstractClosureExpr, 2,
    /// If the autoclosure was built for a curry thunk, the thunk kind is
    /// stored here.
    Kind : 2
  );

  SWIFT_INLINE_BITFIELD(ClosureExpr, AbstractClosureExpr, 1,
    /// True if closure parameters were synthesized from anonymous closure
    /// variables.
    HasAnonymousClosureVars : 1
  );

  SWIFT_INLINE_BITFIELD_FULL(BindOptionalExpr, Expr, 16,
    : NumPadBits,
    Depth : 16
  );

  SWIFT_INLINE_BITFIELD_EMPTY(ImplicitConversionExpr, Expr);

  SWIFT_INLINE_BITFIELD_FULL(DestructureTupleExpr, ImplicitConversionExpr, 16,
    /// The number of elements in the tuple type being destructured.
    NumElements : 16
  );

  SWIFT_INLINE_BITFIELD(ForceValueExpr, Expr, 1,
    ForcedIUO : 1
  );

  SWIFT_INLINE_BITFIELD(InOutToPointerExpr, ImplicitConversionExpr, 1,
    IsNonAccessing : 1
  );

  SWIFT_INLINE_BITFIELD(ArrayToPointerExpr, ImplicitConversionExpr, 1,
    IsNonAccessing : 1
  );

  SWIFT_INLINE_BITFIELD_FULL(ErasureExpr, ImplicitConversionExpr, 32,
    : NumPadBits,
    NumConformances : 32
  );

  SWIFT_INLINE_BITFIELD_FULL(UnresolvedSpecializeExpr, Expr, 32,
    : NumPadBits,
    NumUnresolvedParams : 32
  );

  SWIFT_INLINE_BITFIELD_FULL(CaptureListExpr, Expr, 32,
    : NumPadBits,
    NumCaptures : 32
  );

  SWIFT_INLINE_BITFIELD(ApplyExpr, Expr, 1+1+1,
    ThrowsIsSet : 1,
    Throws : 1,
    ImplicitlyAsync : 1
  );

  SWIFT_INLINE_BITFIELD_FULL(CallExpr, ApplyExpr, 1+1+16,
    /// Whether the CallExpr also has source locations for the argument label.
    HasArgLabelLocs : 1,
    /// Whether the last argument is a trailing closure.
    HasTrailingClosure : 1,
    : NumPadBits,
    /// # of argument labels stored after the CallExpr.
    NumArgLabels : 16
  );

  enum { NumCheckedCastKindBits = 4 };
  SWIFT_INLINE_BITFIELD(CheckedCastExpr, Expr, NumCheckedCastKindBits,
    CastKind : NumCheckedCastKindBits
  );
  static_assert(unsigned(CheckedCastKind::Last_CheckedCastKind)
                  < (1 << NumCheckedCastKindBits),
                "unable to fit a CheckedCastKind in the given number of bits");

  SWIFT_INLINE_BITFIELD_EMPTY(CollectionUpcastConversionExpr, Expr);

  SWIFT_INLINE_BITFIELD(ObjCSelectorExpr, Expr, 2,
    /// The selector kind.
    SelectorKind : 2
  );

  SWIFT_INLINE_BITFIELD(KeyPathExpr, Expr, 1,
    /// Whether this is an ObjC stringified keypath.
    IsObjC : 1
  );

  SWIFT_INLINE_BITFIELD_FULL(SequenceExpr, Expr, 32,
    : NumPadBits,
    NumElements : 32
  );

  SWIFT_INLINE_BITFIELD(OpaqueValueExpr, Expr, 1,
    IsPlaceholder : 1
  );

  } Bits;

private:
  /// Ty - This is the type of the expression.
  Type Ty;
 
protected:
  Expr(ExprKind Kind, bool Implicit, Type Ty = Type()) : Ty(Ty) {
    Bits.OpaqueBits = 0;
    Bits.Expr.Kind = unsigned(Kind);
    Bits.Expr.Implicit = Implicit;
  }

public:
  /// Return the kind of this expression.
  ExprKind getKind() const { return ExprKind(Bits.Expr.Kind); }

  /// Retrieve the name of the given expression kind.
  ///
  /// This name should only be used for debugging dumps and other
  /// developer aids, and should never be part of a diagnostic or exposed
  /// to the user of the compiler in any way.
  static StringRef getKindName(ExprKind K);

  /// getType - Return the type of this expression.
  Type getType() const { return Ty; }

  /// setType - Sets the type of this expression.
  void setType(Type T);

  /// Return the source range of the expression.
  SourceRange getSourceRange() const;
  
  /// getStartLoc - Return the location of the start of the expression.
  SourceLoc getStartLoc() const;

  /// Retrieve the location of the last token of the expression.
  SourceLoc getEndLoc() const;
  
  /// getLoc - Return the caret location of this expression.
  SourceLoc getLoc() const;

#define SWIFT_FORWARD_SOURCE_LOCS_TO(SUBEXPR) \
  SourceLoc getStartLoc() const { return (SUBEXPR)->getStartLoc(); } \
  SourceLoc getEndLoc() const { return (SUBEXPR)->getEndLoc(); } \
  SourceLoc getLoc() const { return (SUBEXPR)->getLoc(); } \
  SourceRange getSourceRange() const { return (SUBEXPR)->getSourceRange(); }

  SourceLoc TrailingSemiLoc;

  /// getSemanticsProvidingExpr - Find the smallest subexpression
  /// which obeys the property that evaluating it is exactly
  /// equivalent to evaluating this expression.
  ///
  /// Looks through parentheses.  Would not look through something
  /// like '(foo(), x:bar(), baz()).x'.
  Expr *getSemanticsProvidingExpr();

  const Expr *getSemanticsProvidingExpr() const {
    return const_cast<Expr *>(this)->getSemanticsProvidingExpr();
  }

  /// getValueProvidingExpr - Find the smallest subexpression which is
  /// responsible for generating the value of this expression.
  /// Evaluating the result is not necessarily equivalent to
  /// evaluating this expression because of potential missing
  /// side-effects (which may influence the returned value).
  Expr *getValueProvidingExpr();

  const Expr *getValueProvidingExpr() const {
    return const_cast<Expr *>(this)->getValueProvidingExpr();
  }

  /// If this is a reference to an operator written as a member of a type (or
  /// extension thereof), return the underlying operator reference.
  DeclRefExpr *getMemberOperatorRef();

  /// This recursively walks the AST rooted at this expression.
  Expr *walk(ASTWalker &walker);
  Expr *walk(ASTWalker &&walker) { return walk(walker); }

  /// Enumerate each immediate child expression of this node, invoking the
  /// specific functor on it.  This ignores statements and other non-expression
  /// children.
  void forEachImmediateChildExpr(llvm::function_ref<Expr *(Expr *)> callback);

  /// Enumerate each expr node within this expression subtree, invoking the
  /// specific functor on it.  This ignores statements and other non-expression
  /// children, and if there is a closure within the expression, this does not
  /// walk into the body of it (unless it is single-expression).
  void forEachChildExpr(llvm::function_ref<Expr *(Expr *)> callback);

  /// Determine whether this expression refers to a type by name.
  ///
  /// This distinguishes static references to types, like Int, from metatype
  /// values, "someTy: Any.Type".
  bool isTypeReference(
      llvm::function_ref<Type(Expr *)> getType = [](Expr *E) -> Type {
        return E->getType();
      },
      llvm::function_ref<Decl *(Expr *)> getDecl = [](Expr *E) -> Decl * {
        return nullptr;
      }) const;

  /// Determine whether this expression refers to a statically-derived metatype.
  ///
  /// This implies `isTypeReference`, but also requires that the referenced type
  /// is not an archetype or dependent type.
  bool isStaticallyDerivedMetatype(
      llvm::function_ref<Type(Expr *)> getType = [](Expr *E) -> Type {
        return E->getType();
      },
      llvm::function_ref<bool(Expr *)> isTypeReference =
          [](Expr *E) { return E->isTypeReference(); }) const;

  /// isImplicit - Determines whether this expression was implicitly-generated,
  /// rather than explicitly written in the AST.
  bool isImplicit() const {
    return Bits.Expr.Implicit;
  }
  void setImplicit(bool Implicit = true);

  /// Retrieves the declaration that is being referenced by this
  /// expression, if any.
  ConcreteDeclRef getReferencedDecl(bool stopAtParenExpr = false) const;

  /// Determine whether this expression is 'super', possibly converted to
  /// a base class.
  bool isSuperExpr() const;

  /// Returns whether the semantically meaningful content of this expression is
  /// an inout expression.
  ///
  /// FIXME(Remove InOutType): This should eventually sub-in for
  /// 'E->getType()->is<InOutType>()' in all cases.
  bool isSemanticallyInOutExpr() const {
    return getSemanticsProvidingExpr()->getKind() == ExprKind::InOut;
  }
  
  /// Returns false if this expression needs to be wrapped in parens when
  /// used inside of a any postfix expression, true otherwise.
  ///
  /// \param appendingPostfixOperator if the expression being
  /// appended is a postfix operator like '!' or '?'.
  bool canAppendPostfixExpression(bool appendingPostfixOperator = false) const;

  /// Returns true if this is an infix operator of some sort, including
  /// a builtin operator.
  bool isInfixOperator() const;

  /// Returns true if this is a reference to the implicit self of function.
  bool isSelfExprOf(const AbstractFunctionDecl *AFD,
                    bool sameBase = false) const;

  /// Given that this is a packed argument expression of the sort that
  /// would be produced from packSingleArgument, return the index of the
  /// unlabeled trailing closure, if there is one.
  Optional<unsigned> getUnlabeledTrailingClosureIndexOfPackedArgument() const;

  /// Produce a mapping from each subexpression to its parent
  /// expression, with the provided expression serving as the root of
  /// the parent map.
  llvm::DenseMap<Expr *, Expr *> getParentMap();

  SWIFT_DEBUG_DUMP;
  void dump(raw_ostream &OS, unsigned Indent = 0) const;
  void dump(raw_ostream &OS, llvm::function_ref<Type(Expr *)> getType,
            llvm::function_ref<Type(TypeRepr *)> getTypeOfTypeRepr,
            llvm::function_ref<Type(KeyPathExpr *E, unsigned index)>
                getTypeOfKeyPathComponent,
            unsigned Indent = 0) const;

  void print(ASTPrinter &Printer, const PrintOptions &Opts) const;

  // Only allow allocation of Exprs using the allocator in ASTContext
  // or by doing a placement new.
  void *operator new(size_t Bytes, ASTContext &C,
                     unsigned Alignment = alignof(Expr));

  // Make placement new and vanilla new/delete illegal for Exprs.
  void *operator new(size_t Bytes) throw() = delete;
  void operator delete(void *Data) throw() = delete;

  void *operator new(size_t Bytes, void *Mem) { 
    assert(Mem); 
    return Mem; 
  }
};

/// ErrorExpr - Represents a semantically erroneous subexpression in the AST,
/// typically this will have an ErrorType.
class ErrorExpr : public Expr {
  SourceRange Range;
  Expr *OriginalExpr;
public:
  ErrorExpr(SourceRange Range, Type Ty = Type(), Expr *OriginalExpr = nullptr)
    : Expr(ExprKind::Error, /*Implicit=*/true, Ty), Range(Range),
      OriginalExpr(OriginalExpr) {}

  SourceRange getSourceRange() const { return Range; }
  Expr *getOriginalExpr() const { return OriginalExpr; }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::Error;
  }
};

/// CodeCompletionExpr - Represents the code completion token in the AST, this
/// can help us preserve the context of the code completion position.
class CodeCompletionExpr : public Expr {
  Expr *Base;
  SourceLoc Loc;

public:
  CodeCompletionExpr(Expr *Base, SourceLoc Loc)
      : Expr(ExprKind::CodeCompletion, /*Implicit=*/true, Type()),
        Base(Base), Loc(Loc) {}

  CodeCompletionExpr(SourceLoc Loc)
      : CodeCompletionExpr(/*Base=*/nullptr, Loc) {}

  Expr *getBase() const { return Base; }
  void setBase(Expr *E) { Base = E; }

  SourceLoc getLoc() const { return Loc; }
  SourceLoc getStartLoc() const { return Base ? Base->getStartLoc() : Loc; }
  SourceLoc getEndLoc() const { return Loc; }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::CodeCompletion;
  }
};

/// LiteralExpr - Common base class between the literals.
class LiteralExpr : public Expr {
  // Set by Sema:
  ConcreteDeclRef Initializer;

public:
  LiteralExpr(ExprKind Kind, bool Implicit) : Expr(Kind, Implicit) {}

  static bool classof(const Expr *E) {
    return E->getKind() >= ExprKind::First_LiteralExpr &&
           E->getKind() <= ExprKind::Last_LiteralExpr;
  }

  /// Retrieve the initializer that will be used to construct the
  /// literal from the result of the initializer.
  ///
  /// Only literals that have no builtin literal conformance will have
  /// this initializer, which will be called on the result of the builtin
  /// initializer.
  ConcreteDeclRef getInitializer() const { return Initializer; }

  /// Set the initializer that will be used to construct the literal.
  void setInitializer(ConcreteDeclRef initializer) {
    Initializer = initializer;
  }
};

/// BuiltinLiteralExpr - Common base class between all literals
/// that provides BuiltinInitializer
class BuiltinLiteralExpr : public LiteralExpr {
  // Set by Seam:
  ConcreteDeclRef BuiltinInitializer;

public:
  BuiltinLiteralExpr(ExprKind Kind, bool Implicit)
      : LiteralExpr(Kind, Implicit) {}

  static bool classof(const Expr *E) {
    return E->getKind() >= ExprKind::First_BuiltinLiteralExpr &&
           E->getKind() <= ExprKind::Last_BuiltinLiteralExpr;
  }

  /// Retrieve the builtin initializer that will be used to construct the
  /// literal.
  ///
  /// Any type-checked literal will have a builtin initializer, which is
  /// called first to form a concrete Swift type.
  ConcreteDeclRef getBuiltinInitializer() const { return BuiltinInitializer; }

  /// Set the builtin initializer that will be used to construct the
  /// literal.
  void setBuiltinInitializer(ConcreteDeclRef builtinInitializer) {
    BuiltinInitializer = builtinInitializer;
  }
};

/// The 'nil' literal.
///
class NilLiteralExpr : public LiteralExpr {
  SourceLoc Loc;

public:
  NilLiteralExpr(SourceLoc Loc, bool Implicit = false)
  : LiteralExpr(ExprKind::NilLiteral, Implicit), Loc(Loc) {
  }
  
  SourceRange getSourceRange() const {
    return Loc;
  }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::NilLiteral;
  }
};

/// Abstract base class for numeric literals, potentially with a sign.
class NumberLiteralExpr : public BuiltinLiteralExpr {
  /// The value of the literal as an ASTContext-owned string. Underscores must
  /// be stripped.
  StringRef Val;  // Use StringRef instead of APInt or APFloat, which leak.

protected:
  SourceLoc MinusLoc;
  SourceLoc DigitsLoc;
  
public:
  NumberLiteralExpr(ExprKind Kind, StringRef Val, SourceLoc DigitsLoc,
                    bool Implicit)
      : BuiltinLiteralExpr(Kind, Implicit), Val(Val), DigitsLoc(DigitsLoc) {
    Bits.NumberLiteralExpr.IsNegative = false;
    Bits.NumberLiteralExpr.IsExplicitConversion = false;
  }

  bool isNegative() const { return Bits.NumberLiteralExpr.IsNegative; }
  void setNegative(SourceLoc Loc) {
    MinusLoc = Loc;
    Bits.NumberLiteralExpr.IsNegative = true;
  }

  bool isExplicitConversion() const {
    return Bits.NumberLiteralExpr.IsExplicitConversion;
  }
  void setExplicitConversion(bool isExplicitConversion = true) {
    Bits.NumberLiteralExpr.IsExplicitConversion = isExplicitConversion;
  }

  StringRef getDigitsText() const { return Val; }

  SourceRange getSourceRange() const {
    if (isNegative())
      return { MinusLoc, DigitsLoc };
    else
      return DigitsLoc;
  }

  SourceLoc getMinusLoc() const {
    return MinusLoc;
  }

  SourceLoc getDigitsLoc() const {
    return DigitsLoc;
  }

  static bool classof(const Expr *E) {
    return E->getKind() >= ExprKind::First_NumberLiteralExpr
      && E->getKind() <= ExprKind::Last_NumberLiteralExpr;
  }
};

/// Integer literal with a '+' or '-' sign, like '+4' or '- 2'.
///
/// After semantic analysis assigns types, this is guaranteed to have
/// a BuiltinIntegerType or be a normal type and implicitly be
/// AnyBuiltinIntegerType.
class IntegerLiteralExpr : public NumberLiteralExpr {
public:
  IntegerLiteralExpr(StringRef Val, SourceLoc DigitsLoc, bool Implicit = false)
      : NumberLiteralExpr(ExprKind::IntegerLiteral,
                          Val, DigitsLoc, Implicit)
  {}

  /// Returns a new integer literal expression with the given value.
  /// \p C The AST context.
  /// \p value The integer value.
  /// \return An implicit integer literal expression which evaluates to the value.
  static IntegerLiteralExpr *
  createFromUnsigned(ASTContext &C, unsigned value);

  /// Returns the value of the literal, appropriately constructed in the
  /// target type.
  APInt getValue() const;

  /// Returns the raw value of the literal without any truncation.
  APInt getRawValue() const;

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::IntegerLiteral;
  }
};

/// FloatLiteralExpr - Floating point literal, like '4.0'.  After semantic
/// analysis assigns types, BuiltinTy is guaranteed to only have a
/// BuiltinFloatingPointType.
class FloatLiteralExpr : public NumberLiteralExpr {
  /// This is the type of the builtin literal.
  Type BuiltinTy;

public:
  FloatLiteralExpr(StringRef Val, SourceLoc Loc, bool Implicit = false)
    : NumberLiteralExpr(ExprKind::FloatLiteral, Val, Loc, Implicit)
  {}
  
  APFloat getValue() const;
  static APFloat getValue(StringRef Text, const llvm::fltSemantics &Semantics,
                          bool Negative);
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::FloatLiteral;
  }

  Type getBuiltinType() const { return BuiltinTy; }
  void setBuiltinType(Type ty) { BuiltinTy = ty; }
};

/// A Boolean literal ('true' or 'false')
///
class BooleanLiteralExpr : public BuiltinLiteralExpr {
  SourceLoc Loc;

public:
  BooleanLiteralExpr(bool Value, SourceLoc Loc, bool Implicit = false)
      : BuiltinLiteralExpr(ExprKind::BooleanLiteral, Implicit), Loc(Loc) {
    Bits.BooleanLiteralExpr.Value = Value;
  }

  /// Retrieve the Boolean value of this literal.
  bool getValue() const { return Bits.BooleanLiteralExpr.Value; }

  SourceRange getSourceRange() const {
    return Loc;
  }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::BooleanLiteral;
  }
};

/// StringLiteralExpr - String literal, like '"foo"'.
class StringLiteralExpr : public BuiltinLiteralExpr {
  StringRef Val;
  SourceRange Range;

public:
  /// The encoding that should be used for the string literal.
  enum Encoding : unsigned {
    /// A UTF-8 string.
    UTF8,

    /// A single UnicodeScalar, passed as an integer.
    OneUnicodeScalar
  };

  StringLiteralExpr(StringRef Val, SourceRange Range, bool Implicit = false);

  StringRef getValue() const { return Val; }
  SourceRange getSourceRange() const { return Range; }

  /// Determine the encoding that should be used for this string literal.
  Encoding getEncoding() const {
    return static_cast<Encoding>(Bits.StringLiteralExpr.Encoding);
  }

  /// Set the encoding that should be used for this string literal.
  void setEncoding(Encoding encoding) {
    Bits.StringLiteralExpr.Encoding = static_cast<unsigned>(encoding);
  }

  bool isSingleUnicodeScalar() const {
    return Bits.StringLiteralExpr.IsSingleUnicodeScalar;
  }

  bool isSingleExtendedGraphemeCluster() const {
    return Bits.StringLiteralExpr.IsSingleExtendedGraphemeCluster;
  }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::StringLiteral;
  }
};

/// Runs a series of statements which use or modify \c SubExpr
/// before it is given to the rest of the expression.
///
/// \c Body should begin with a \c VarDecl; this defines the variable
/// \c TapExpr will initialize at the beginning and read a result
/// from at the end. \c TapExpr creates a separate scope, then
/// assigns the result of \c SubExpr to the variable and runs \c Body
/// in it, returning the value of the variable after the \c Body runs.
///
/// (The design here could be a bit cleaner, particularly where the VarDecl
/// is concerned.)
class TapExpr : public Expr {
  Expr *SubExpr;
  BraceStmt *Body;

public:
  TapExpr(Expr *SubExpr, BraceStmt *Body);

  Expr * getSubExpr() const { return SubExpr; }
  void setSubExpr(Expr * se) { SubExpr = se; }

  /// The variable which will be accessed and possibly modified by
  /// the \c Body. This is the first \c ASTNode in the \c Body.
  VarDecl * getVar() const;

  BraceStmt * getBody() const { return Body; }
  void setBody(BraceStmt * b) { Body = b; }

  SourceLoc getLoc() const { return SubExpr ? SubExpr->getLoc() : SourceLoc(); }
  
  SourceLoc getStartLoc() const {
    return SubExpr ? SubExpr->getStartLoc() : SourceLoc();
  }

  SourceLoc getEndLoc() const;

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::Tap;
  }
};

/// InterpolatedStringLiteral - An interpolated string literal.
///
/// An interpolated string literal mixes expressions (which are evaluated and
/// converted into string form) within a string literal.
///
/// \code
/// "[\(min)..\(max)]"
/// \endcode
class InterpolatedStringLiteralExpr : public LiteralExpr {
  /// Points at the beginning quote.
  SourceLoc Loc;
  /// Points at the ending quote.
  /// Needed for the upcoming \c ASTScope subsystem because lookups can be
  /// targeted to inside an \c InterpolatedStringLiteralExpr. It would be nicer
  /// to use \c EndLoc for this value, but then \c Lexer::getLocForEndOfToken()
  /// would not work for \c stringLiteral->getEndLoc().
  SourceLoc TrailingQuoteLoc;
  TapExpr *AppendingExpr;

  // Set by Sema:
  OpaqueValueExpr *interpolationExpr = nullptr;
  ConcreteDeclRef builderInit;
  Expr *interpolationCountExpr = nullptr;
  Expr *literalCapacityExpr = nullptr;

public:
  InterpolatedStringLiteralExpr(SourceLoc Loc,
                                SourceLoc TrailingQuoteLoc,
                                unsigned LiteralCapacity,
                                unsigned InterpolationCount,
                                TapExpr *AppendingExpr)
      : LiteralExpr(ExprKind::InterpolatedStringLiteral, /*Implicit=*/false),
        Loc(Loc),
        TrailingQuoteLoc(TrailingQuoteLoc),
        AppendingExpr(AppendingExpr) {
    Bits.InterpolatedStringLiteralExpr.InterpolationCount = InterpolationCount;
    Bits.InterpolatedStringLiteralExpr.LiteralCapacity = LiteralCapacity;
  }

  // Sets the constructor for the interpolation type.
  void setBuilderInit(ConcreteDeclRef decl) { builderInit = decl; }
  ConcreteDeclRef getBuilderInit() const { return builderInit; }

  /// Sets the OpaqueValueExpr that is passed into AppendingExpr as the SubExpr
  /// that the tap operates on.
  void setInterpolationExpr(OpaqueValueExpr *expr) { interpolationExpr = expr; }
  OpaqueValueExpr *getInterpolationExpr() const { return interpolationExpr; }

  /// Store a builtin integer literal expr wrapping getInterpolationCount().
  /// This is an arg to builderInit.
  void setInterpolationCountExpr(Expr *expr) { interpolationCountExpr = expr; }
  Expr *getInterpolationCountExpr() const { return interpolationCountExpr; }

  /// Store a builtin integer literal expr wrapping getLiteralCapacity().
  /// This is an arg to builderInit.
  void setLiteralCapacityExpr(Expr *expr) { literalCapacityExpr = expr; }
  Expr *getLiteralCapacityExpr() const { return literalCapacityExpr; }

  /// Retrieve the value of the literalCapacity parameter to the
  /// initializer.
  unsigned getLiteralCapacity() const {
    return Bits.InterpolatedStringLiteralExpr.LiteralCapacity;
  }

  /// Retrieve the value of the interpolationCount parameter to the
  /// initializer.
  unsigned getInterpolationCount() const {
    return Bits.InterpolatedStringLiteralExpr.InterpolationCount;
  }

  /// A block containing expressions which call
  /// \c StringInterpolationProtocol methods to append segments to the
  /// string interpolation. The first node in \c Body should be an uninitialized
  /// \c VarDecl; the other statements should append to it.
  TapExpr * getAppendingExpr() const { return AppendingExpr; }
  void setAppendingExpr(TapExpr * AE) { AppendingExpr = AE; }
  
  SourceLoc getStartLoc() const {
    return Loc;
  }
  SourceLoc getEndLoc() const {
    // SourceLocs are token based, and the interpolated string is one string
    // token, so the range should be (Start == End).
    return Loc;
  }
  
  /// Could also be computed by relexing.
  SourceLoc getTrailingQuoteLoc() const {
    return TrailingQuoteLoc;
  }

  /// Call the \c callback with information about each segment in turn.
  void forEachSegment(ASTContext &Ctx,
                      llvm::function_ref<void(bool, CallExpr *)> callback);
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::InterpolatedStringLiteral;
  }
};
  
/// MagicIdentifierLiteralExpr - A magic identifier like #file which expands
/// out to a literal at SILGen time.
class MagicIdentifierLiteralExpr : public BuiltinLiteralExpr {
public:
  enum Kind : unsigned {
#define MAGIC_IDENTIFIER(NAME, STRING, SYNTAX_KIND) NAME,
#include "swift/AST/MagicIdentifierKinds.def"
  };

  static StringRef getKindString(MagicIdentifierLiteralExpr::Kind value) {
    switch (value) {
#define MAGIC_IDENTIFIER(NAME, STRING, SYNTAX_KIND) case NAME: return STRING;
#include "swift/AST/MagicIdentifierKinds.def"
    }

    llvm_unreachable("Unhandled MagicIdentifierLiteralExpr in getKindString.");
  }

private:
  SourceLoc Loc;

public:
  MagicIdentifierLiteralExpr(Kind kind, SourceLoc loc, bool implicit = false)
      : BuiltinLiteralExpr(ExprKind::MagicIdentifierLiteral, implicit),
        Loc(loc) {
    Bits.MagicIdentifierLiteralExpr.Kind = static_cast<unsigned>(kind);
    Bits.MagicIdentifierLiteralExpr.StringEncoding
      = static_cast<unsigned>(StringLiteralExpr::UTF8);
  }

  Kind getKind() const {
    return static_cast<Kind>(Bits.MagicIdentifierLiteralExpr.Kind);
  }

  bool isString() const {
    switch (getKind()) {
#define MAGIC_STRING_IDENTIFIER(NAME, STRING, SYNTAX_KIND) \
    case NAME: \
      return true;
#define MAGIC_IDENTIFIER(NAME, STRING, SYNTAX_KIND) \
    case NAME: \
      return false;
#include "swift/AST/MagicIdentifierKinds.def"
    }
    llvm_unreachable("bad Kind");
  }

  SourceRange getSourceRange() const { return Loc; }

  // For a magic identifier that produces a string literal, retrieve the
  // encoding for that string literal.
  StringLiteralExpr::Encoding getStringEncoding() const {
    assert(isString() && "Magic identifier literal has non-string encoding");
    return static_cast<StringLiteralExpr::Encoding>(
             Bits.MagicIdentifierLiteralExpr.StringEncoding);
  }

  // For a magic identifier that produces a string literal, set the encoding
  // for the string literal.
  void setStringEncoding(StringLiteralExpr::Encoding encoding) {
    assert(isString() && "Magic identifier literal has non-string encoding");
    Bits.MagicIdentifierLiteralExpr.StringEncoding
      = static_cast<unsigned>(encoding);
  }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::MagicIdentifierLiteral;
  }
};

// ObjectLiteralExpr - An expression of the form
// '#colorLiteral(red: 1, blue: 0, green: 0, alpha: 1)' with a name and a list
// argument. The components of the list argument are meant to be themselves
// constant.
class ObjectLiteralExpr final
    : public LiteralExpr,
      public TrailingCallArguments<ObjectLiteralExpr> {
public:
  /// The kind of object literal.
  enum LiteralKind : unsigned {
#define POUND_OBJECT_LITERAL(Name, Desc, Proto) Name,
#include "swift/Syntax/TokenKinds.def"
  };

private:
  Expr *Arg;
  SourceLoc PoundLoc;

  ObjectLiteralExpr(SourceLoc PoundLoc, LiteralKind LitKind,
                    Expr *Arg,
                    ArrayRef<Identifier> argLabels,
                    ArrayRef<SourceLoc> argLabelLocs,
                    bool hasTrailingClosure,
                    bool implicit);

public:
  /// Create a new object literal expression.
  ///
  /// Note: prefer to use the second entry point, which separates out
  /// arguments/labels/etc.
  static ObjectLiteralExpr *create(ASTContext &ctx, SourceLoc poundLoc,
                                   LiteralKind kind, Expr *arg, bool implicit,
                                   llvm::function_ref<Type(Expr *)> getType);

  /// Create a new object literal expression.
  static ObjectLiteralExpr *create(ASTContext &ctx, SourceLoc poundLoc,
                                   LiteralKind kind,
                                   SourceLoc lParenLoc,
                                   ArrayRef<Expr *> args,
                                   ArrayRef<Identifier> argLabels,
                                   ArrayRef<SourceLoc> argLabelLocs,
                                   SourceLoc rParenLoc,
                                   ArrayRef<TrailingClosure> trailingClosures,
                                   bool implicit);

  LiteralKind getLiteralKind() const {
    return static_cast<LiteralKind>(Bits.ObjectLiteralExpr.LitKind);
  }

  Expr *getArg() const { return Arg; }
  void setArg(Expr *arg) { Arg = arg; }

  unsigned getNumArguments() const {
    return Bits.ObjectLiteralExpr.NumArgLabels;
  }
  bool hasArgumentLabelLocs() const {
    return Bits.ObjectLiteralExpr.HasArgLabelLocs;
  }

  /// Whether this call with written with a trailing closure.
  bool hasTrailingClosure() const {
    return Bits.ObjectLiteralExpr.HasTrailingClosure;
  }

  /// Return the index of the unlabeled trailing closure argument.
  Optional<unsigned> getUnlabeledTrailingClosureIndex() const {
    return getArg()->getUnlabeledTrailingClosureIndexOfPackedArgument();
  }

  SourceLoc getSourceLoc() const { return PoundLoc; }
  SourceRange getSourceRange() const { 
    return SourceRange(PoundLoc, Arg->getEndLoc());
  }

  /// Return the string form of the literal name.
  StringRef getLiteralKindRawName() const;

  StringRef getLiteralKindPlainName() const;

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::ObjectLiteral;
  }
};

/// DiscardAssignmentExpr - A '_' in the left-hand side of an assignment, which
/// discards the corresponding tuple element on the right-hand side.
class DiscardAssignmentExpr : public Expr {
  SourceLoc Loc;

public:
  DiscardAssignmentExpr(SourceLoc Loc, bool Implicit)
    : Expr(ExprKind::DiscardAssignment, Implicit), Loc(Loc) {}
  
  SourceRange getSourceRange() const { return Loc; }
  SourceLoc getLoc() const { return Loc; }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::DiscardAssignment;
  }
};

/// DeclRefExpr - A reference to a value, "x".
class DeclRefExpr : public Expr {
  /// The declaration pointer.
  ConcreteDeclRef D;
  DeclNameLoc Loc;

public:
  DeclRefExpr(ConcreteDeclRef D, DeclNameLoc Loc, bool Implicit,
              AccessSemantics semantics = AccessSemantics::Ordinary,
              Type Ty = Type())
    : Expr(ExprKind::DeclRef, Implicit, Ty), D(D), Loc(Loc) {
    Bits.DeclRefExpr.Semantics = (unsigned) semantics;
    Bits.DeclRefExpr.FunctionRefKind =
      static_cast<unsigned>(Loc.isCompound() ? FunctionRefKind::Compound
                                             : FunctionRefKind::Unapplied);
  }

  /// Retrieve the declaration to which this expression refers.
  ValueDecl *getDecl() const {
    return getDeclRef().getDecl();
  }

  /// Return true if this access is direct, meaning that it does not call the
  /// getter or setter.
  AccessSemantics getAccessSemantics() const {
    return (AccessSemantics) Bits.DeclRefExpr.Semantics;
  }

  /// Retrieve the concrete declaration reference.
  ConcreteDeclRef getDeclRef() const {
    return D;
  }

  SourceRange getSourceRange() const { return Loc.getSourceRange(); }
  SourceLoc getLoc() const { return Loc.getBaseNameLoc(); }
  DeclNameLoc getNameLoc() const { return Loc; }

  /// Retrieve the kind of function reference.
  FunctionRefKind getFunctionRefKind() const {
    return static_cast<FunctionRefKind>(Bits.DeclRefExpr.FunctionRefKind);
  }

  /// Set the kind of function reference.
  void setFunctionRefKind(FunctionRefKind refKind) {
    Bits.DeclRefExpr.FunctionRefKind = static_cast<unsigned>(refKind);
  }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::DeclRef;
  }
};
  
/// A reference to 'super'. References to members of 'super' resolve to members
/// of a superclass of 'self'.
class SuperRefExpr : public Expr {
  VarDecl *Self;
  SourceLoc Loc;
  
public:
  SuperRefExpr(VarDecl *Self, SourceLoc Loc, bool Implicit,
               Type SuperTy = Type())
    : Expr(ExprKind::SuperRef, Implicit, SuperTy), Self(Self), Loc(Loc) {}
  
  VarDecl *getSelf() const { return Self; }
  void setSelf(VarDecl *self) { Self = self; }
  
  SourceLoc getSuperLoc() const { return Loc; }
  SourceRange getSourceRange() const { return Loc; }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::SuperRef;
  }
};

/// A reference to a type in expression context.
///
/// The type of this expression is always \c MetatypeType.
class TypeExpr : public Expr {
  TypeRepr *Repr;
public:
  /// Create a \c TypeExpr from a parsed \c TypeRepr.
  TypeExpr(TypeRepr *Ty);

  /// Retrieves the corresponding instance type of the type referenced by this
  /// expression.
  ///
  /// If this node has no type, the resulting instance type is also the
  /// null \c Type(). If the type of this node is not a \c MetatypeType, the
  /// resulting instance type is \c ErrorType.
  Type getInstanceType() const;

public:
  /// Create an implicit \c TypeExpr.
  ///
  /// The given type is required to be non-null and must be not be
  /// a \c MetatypeType as this function will wrap the given type in one.
  ///
  /// FIXME: This behavior is bizarre.
  static TypeExpr *createImplicit(Type Ty, ASTContext &C);

  /// Create an implicit \c TypeExpr that has artificial
  /// location information attached.
  ///
  /// The given type is required to be non-null and must be not be
  /// a \c MetatypeType as this function will wrap the given type in one.
  ///
  /// FIXME: This behavior is bizarre.
  ///
  /// Due to limitations in the modeling of certain AST elements, implicit
  /// \c TypeExpr nodes are often the only source of location information the
  /// expression checker has when it comes time to diagnose an error.
  static TypeExpr *createImplicitHack(SourceLoc Loc, Type Ty, ASTContext &C);

  /// Create an implicit \c TypeExpr for a given \c TypeDecl at the specified location.
  ///
  /// The given type is required to be non-null and must be not be
  /// a \c MetatypeType as this function will wrap the given type in one.
  ///
  /// FIXME: This behavior is bizarre.
  ///
  /// Unlike the non-implicit case, the given location is not required to be
  /// valid.
  static TypeExpr *createImplicitForDecl(DeclNameLoc Loc, TypeDecl *D,
                                         DeclContext *DC, Type ty);

public:
  /// Create a \c TypeExpr for a given \c TypeDecl at the specified location.
  ///
  /// The given location must be valid. If it is not, you must use
  /// \c TypeExpr::createImplicitForDecl instead.
  static TypeExpr *createForDecl(DeclNameLoc Loc, TypeDecl *D, DeclContext *DC);

  /// Create a TypeExpr for a member TypeDecl of the given parent TypeDecl.
  static TypeExpr *createForMemberDecl(DeclNameLoc ParentNameLoc,
                                       TypeDecl *Parent,
                                       DeclNameLoc NameLoc,
                                       TypeDecl *Decl);

  /// Create a TypeExpr for a member TypeDecl of the given parent IdentTypeRepr.
  static TypeExpr *createForMemberDecl(IdentTypeRepr *ParentTR,
                                       DeclNameLoc NameLoc,
                                       TypeDecl *Decl);

  /// Create a TypeExpr from an IdentTypeRepr with the given arguments applied
  /// at the specified location.
  ///
  /// Returns nullptr if the reference cannot be formed, which is a hack due
  /// to limitations in how we model generic typealiases.
  static TypeExpr *createForSpecializedDecl(IdentTypeRepr *ParentTR,
                                            ArrayRef<TypeRepr*> Args,
                                            SourceRange AngleLocs,
                                            ASTContext &C);

  TypeRepr *getTypeRepr() const { return Repr; }
  // NOTE: TypeExpr::getType() returns the type of the expr node, which is the
  // metatype of what is stored as an operand type.
  
  SourceRange getSourceRange() const;
  // TODO: optimize getStartLoc() and getEndLoc() when TypeLoc allows it.

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::Type;
  }
};
  
  

/// A reference to another initializer from within a constructor body,
/// either to a delegating initializer or to a super.init invocation.
/// For a reference type, this semantically references a different constructor
/// entry point, called the 'initializing constructor', from the 'allocating
/// constructor' entry point referenced by a 'new' expression.
class OtherConstructorDeclRefExpr : public Expr {
  ConcreteDeclRef Ctor;
  DeclNameLoc Loc;
  
public:
  OtherConstructorDeclRefExpr(ConcreteDeclRef Ctor, DeclNameLoc Loc,
                              bool Implicit, Type Ty = {})
    : Expr(ExprKind::OtherConstructorDeclRef, Implicit, Ty),
      Ctor(Ctor), Loc(Loc)
  {}
  
  ConstructorDecl *getDecl() const;
  ConcreteDeclRef getDeclRef() const { return Ctor; }

  SourceLoc getLoc() const { return Loc.getBaseNameLoc(); }
  DeclNameLoc getConstructorLoc() const { return Loc; }
  SourceRange getSourceRange() const { return Loc.getSourceRange(); }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::OtherConstructorDeclRef;
  }
};

/// OverloadSetRefExpr - A reference to an overloaded set of values with a
/// single name.
///
/// This is an abstract class that covers the various different kinds of
/// overload sets.
class OverloadSetRefExpr : public Expr {
  ArrayRef<ValueDecl*> Decls;

protected:
  OverloadSetRefExpr(ExprKind Kind, ArrayRef<ValueDecl*> decls,
                     FunctionRefKind functionRefKind, bool Implicit, Type Ty)
      : Expr(Kind, Implicit, Ty), Decls(decls) {
    Bits.OverloadSetRefExpr.FunctionRefKind =
      static_cast<unsigned>(functionRefKind);
  }

public:
  ArrayRef<ValueDecl*> getDecls() const { return Decls; }

  void setDecls(ArrayRef<ValueDecl *> domain) {
    Decls = domain;
  }

  /// getBaseType - Determine the type of the base object provided for the
  /// given overload set, which is only non-null when dealing with an overloaded
  /// member reference.
  Type getBaseType() const;

  /// hasBaseObject - Determine whether this overloaded expression has a
  /// concrete base object (which is not a metatype).
  bool hasBaseObject() const;

  /// Retrieve the kind of function reference.
  FunctionRefKind getFunctionRefKind() const {
    return static_cast<FunctionRefKind>(
             Bits.OverloadSetRefExpr.FunctionRefKind);
  }

  /// Set the kind of function reference.
  void setFunctionRefKind(FunctionRefKind refKind) {
    Bits.OverloadSetRefExpr.FunctionRefKind = static_cast<unsigned>(refKind);
  }

  static bool classof(const Expr *E) {
    return E->getKind() >= ExprKind::First_OverloadSetRefExpr &&
           E->getKind() <= ExprKind::Last_OverloadSetRefExpr;
  }
};

/// OverloadedDeclRefExpr - A reference to an overloaded name that should
/// eventually be resolved (by overload resolution) to a value reference.
class OverloadedDeclRefExpr final : public OverloadSetRefExpr {
  DeclNameLoc Loc;

public:
  OverloadedDeclRefExpr(ArrayRef<ValueDecl*> Decls, DeclNameLoc Loc,
                        FunctionRefKind functionRefKind,
                        bool Implicit, Type Ty = Type())
      : OverloadSetRefExpr(ExprKind::OverloadedDeclRef, Decls, functionRefKind,
                           Implicit, Ty),
        Loc(Loc) {
  }
  
  DeclNameLoc getNameLoc() const { return Loc; }
  SourceLoc getLoc() const { return Loc.getBaseNameLoc(); }
  SourceRange getSourceRange() const { return Loc.getSourceRange(); }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::OverloadedDeclRef;
  }
};

/// UnresolvedDeclRefExpr - This represents use of an undeclared identifier,
/// which may ultimately be a use of something that hasn't been defined yet, it
/// may be a use of something that got imported (which will be resolved during
/// sema), or may just be a use of an unknown identifier.
///
class UnresolvedDeclRefExpr : public Expr {
  DeclNameRef Name;
  DeclNameLoc Loc;

public:
  UnresolvedDeclRefExpr(DeclNameRef name, DeclRefKind refKind, DeclNameLoc loc)
      : Expr(ExprKind::UnresolvedDeclRef, /*Implicit=*/loc.isInvalid()),
        Name(name), Loc(loc) {
    Bits.UnresolvedDeclRefExpr.DeclRefKind = static_cast<unsigned>(refKind);
    Bits.UnresolvedDeclRefExpr.FunctionRefKind =
      static_cast<unsigned>(Loc.isCompound() ? FunctionRefKind::Compound
                                             : FunctionRefKind::Unapplied);
  }

  static UnresolvedDeclRefExpr *createImplicit(
      ASTContext &C, DeclName name,
      DeclRefKind refKind = DeclRefKind::Ordinary) {
    return new (C) UnresolvedDeclRefExpr(DeclNameRef(name), refKind,
                                         DeclNameLoc());
  }

  static UnresolvedDeclRefExpr *createImplicit(
      ASTContext &C, DeclBaseName baseName, ArrayRef<Identifier> argLabels) {
    return UnresolvedDeclRefExpr::createImplicit(C,
        DeclName(C, baseName, argLabels));
  }

  static UnresolvedDeclRefExpr *createImplicit(
      ASTContext &C, DeclBaseName baseName, ParameterList *paramList) {
    return UnresolvedDeclRefExpr::createImplicit(C,
        DeclName(C, baseName, paramList));
  }

  bool hasName() const { return static_cast<bool>(Name); }
  DeclNameRef getName() const { return Name; }

  DeclRefKind getRefKind() const {
    return static_cast<DeclRefKind>(Bits.UnresolvedDeclRefExpr.DeclRefKind);
  }

  /// Retrieve the kind of function reference.
  FunctionRefKind getFunctionRefKind() const {
    return static_cast<FunctionRefKind>(
             Bits.UnresolvedDeclRefExpr.FunctionRefKind);
  }

  /// Set the kind of function reference.
  void setFunctionRefKind(FunctionRefKind refKind) {
    Bits.UnresolvedDeclRefExpr.FunctionRefKind = static_cast<unsigned>(refKind);
  }

  DeclNameLoc getNameLoc() const { return Loc; }

  SourceRange getSourceRange() const { return Loc.getSourceRange(); }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::UnresolvedDeclRef;
  }
};

/// LookupExpr - This abstract class represents 'a.b', 'a[]', etc where we
/// are referring to a member of a type, such as a property, variable, etc.
class LookupExpr : public Expr {
  Expr *Base;
  ConcreteDeclRef Member;

protected:
  explicit LookupExpr(ExprKind Kind, Expr *base, ConcreteDeclRef member,
                          bool Implicit)
      : Expr(Kind, Implicit), Base(base), Member(member) {
    Bits.LookupExpr.IsSuper = false;
    assert(Base);
  }

public:
  /// Retrieve the base of the expression.
  Expr *getBase() const { return Base; }

  /// Replace the base of the expression.
  void setBase(Expr *E) { Base = E; }

  /// Retrieve the member to which this access refers.
  ConcreteDeclRef getMember() const { return Member; }

  /// Determine whether the operation has a known underlying declaration or not.
  bool hasDecl() const { return static_cast<bool>(Member); }
  
  /// Retrieve the declaration that this /// operation refers to.
  /// Only valid when \c hasDecl() is true.
  ConcreteDeclRef getDecl() const {
    assert(hasDecl() && "No subscript declaration known!");
    return getMember();
  }

  /// Determine whether this reference refers to the superclass's property.
  bool isSuper() const { return Bits.LookupExpr.IsSuper; }

  /// Set whether this reference refers to the superclass's property.
  void setIsSuper(bool isSuper) { Bits.LookupExpr.IsSuper = isSuper; }

  static bool classof(const Expr *E) {
    return E->getKind() >= ExprKind::First_LookupExpr &&
           E->getKind() <= ExprKind::Last_LookupExpr;
  }
};

/// MemberRefExpr - This represents 'a.b' where we are referring to a member
/// of a type, such as a property or variable.
///
/// Note that methods found via 'dot' syntax are expressed as DotSyntaxCallExpr
/// nodes, because 'a.f' is actually an application of 'a' (the implicit object
/// argument) to the function 'f'.
class MemberRefExpr : public LookupExpr {
  SourceLoc DotLoc;
  DeclNameLoc NameLoc;
  
public:
  MemberRefExpr(Expr *base, SourceLoc dotLoc, ConcreteDeclRef member,
                DeclNameLoc loc, bool Implicit,
                AccessSemantics semantics = AccessSemantics::Ordinary);
  SourceLoc getDotLoc() const { return DotLoc; }
  DeclNameLoc getNameLoc() const { return NameLoc; }
  
  /// Return true if this member access is direct, meaning that it
  /// does not call the getter or setter.
  AccessSemantics getAccessSemantics() const {
    return (AccessSemantics) Bits.MemberRefExpr.Semantics;
  }

  SourceLoc getLoc() const { return NameLoc.getBaseNameLoc(); }
  SourceLoc getStartLoc() const {
    SourceLoc BaseStartLoc = getBase()->getStartLoc();
    if (BaseStartLoc.isInvalid() || NameLoc.isInvalid()) {
      return NameLoc.getBaseNameLoc();
    } else {
      return BaseStartLoc;
    }
  }
  SourceLoc getEndLoc() const {
    return NameLoc.getSourceRange().End;
  }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::MemberRef;
  }
};
  
/// Common base for expressions that involve dynamic lookup, which
/// determines at runtime whether a particular method, property, or
/// subscript is available.
class DynamicLookupExpr : public LookupExpr {
protected:
  explicit DynamicLookupExpr(ExprKind kind, ConcreteDeclRef member, Expr *base)
    : LookupExpr(kind, base, member, /*Implicit=*/false) { }

public:
  static bool classof(const Expr *E) {
    return E->getKind() >= ExprKind::First_DynamicLookupExpr &&
           E->getKind() <= ExprKind::Last_DynamicLookupExpr;
  }
};

/// A reference to a member of an object that was found via dynamic lookup.
///
/// A member found via dynamic lookup may not actually be available at runtime.
/// Therefore, a reference to that member always returns an optional instance.
/// Users can then propagate the optional (via ?) or assert that the member is
/// always available (via !). For example:
///
/// \code
/// class C {
///   func @objc foo(i : Int) -> String { ... }
/// };
///
/// var x : AnyObject = <some value>
/// print(x.foo!(17)) // x.foo has type ((i : Int) -> String)?
/// \endcode
class DynamicMemberRefExpr : public DynamicLookupExpr {
  SourceLoc DotLoc;
  DeclNameLoc NameLoc;

public:
  DynamicMemberRefExpr(Expr *base, SourceLoc dotLoc,
                       ConcreteDeclRef member,
                       DeclNameLoc nameLoc)
    : DynamicLookupExpr(ExprKind::DynamicMemberRef, member, base),
      DotLoc(dotLoc), NameLoc(nameLoc) {
    }

  /// Retrieve the location of the member name.
  DeclNameLoc getNameLoc() const { return NameLoc; }

  /// Retrieve the location of the '.'.
  SourceLoc getDotLoc() const { return DotLoc; }

  SourceLoc getLoc() const { return NameLoc.getBaseNameLoc(); }

  SourceLoc getStartLoc() const {
    SourceLoc BaseStartLoc = getBase()->getStartLoc();
    if (BaseStartLoc.isInvalid() || NameLoc.isInvalid()) {
      return NameLoc.getBaseNameLoc();
    } else {
      return BaseStartLoc;
    }
  }
  SourceLoc getEndLoc() const { return NameLoc.getSourceRange().End; }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::DynamicMemberRef;
  }
};

/// A subscript on an object with dynamic lookup type.
///
/// A subscript found via dynamic lookup may not actually be available
/// at runtime.  Therefore, the result of performing the subscript
/// operation always returns an optional instance.Users can then
/// propagate the optional (via ?) or assert that the member is always
/// available (via !). For example:
///
/// \code
/// class C {
///   @objc subscript (i : Int) -> String {
///     get {
///       ...
///     }
///   }
/// };
///
/// var x : AnyObject = <some value>
/// print(x[27]! // x[27] has type String?
/// \endcode
class DynamicSubscriptExpr final
    : public DynamicLookupExpr,
      public TrailingCallArguments<DynamicSubscriptExpr> {
  friend TrailingCallArguments;

  Expr *Index;

  DynamicSubscriptExpr(Expr *base, Expr *index, ArrayRef<Identifier> argLabels,
                       ArrayRef<SourceLoc> argLabelLocs,
                       bool hasTrailingClosure, ConcreteDeclRef member,
                       bool implicit);

public:
  /// Create a dynamic subscript.
  ///
  /// Note: do not create new callers to this entry point; use the entry point
  /// that takes separate index arguments.
  static DynamicSubscriptExpr *create(
      ASTContext &ctx, Expr *base, Expr *index, ConcreteDeclRef decl,
      bool implicit,
      llvm::function_ref<Type(Expr *)> getType = [](Expr *E) -> Type {
        return E->getType();
      });

  /// getIndex - Retrieve the index of the subscript expression, i.e., the
  /// "offset" into the base value.
  Expr *getIndex() const { return Index; }
  void setIndex(Expr *E) { Index = E; }

  unsigned getNumArguments() const {
    return Bits.DynamicSubscriptExpr.NumArgLabels;
  }

  bool hasArgumentLabelLocs() const {
    return Bits.DynamicSubscriptExpr.HasArgLabelLocs;
  }

  /// Whether this call with written with a trailing closure.
  bool hasTrailingClosure() const {
    return Bits.DynamicSubscriptExpr.HasTrailingClosure;
  }

  /// Return the index of the unlabeled trailing closure argument.
  Optional<unsigned> getUnlabeledTrailingClosureIndex() const {
    return Index->getUnlabeledTrailingClosureIndexOfPackedArgument();
  }

  SourceLoc getLoc() const { return Index->getStartLoc(); }

  SourceLoc getStartLoc() const { return getBase()->getStartLoc(); }
  SourceLoc getEndLoc() const { return Index->getEndLoc(); }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::DynamicSubscript;
  }
};

/// UnresolvedMemberExpr - This represents '.foo', an unresolved reference to a
/// member, which is to be resolved with context sensitive type information into
/// bar.foo.  These always have unresolved type.
class UnresolvedMemberExpr final
    : public Expr {
  SourceLoc DotLoc;
  DeclNameLoc NameLoc;
  DeclNameRef Name;

public:
  UnresolvedMemberExpr(SourceLoc dotLoc, DeclNameLoc nameLoc, DeclNameRef name,
                       bool implicit)
    : Expr(ExprKind::UnresolvedMember, implicit), DotLoc(dotLoc),
      NameLoc(nameLoc), Name(name) {
    // FIXME: Really, we should be setting this to `FunctionRefKind::Compound`
    // if `NameLoc` is compound, but this would be a source break for cases like
    // ```
    // struct S {
    //   static func makeS(_: Int) -> S! { S() }
    // }
    //
    // let s: S = .makeS(_:)(0)
    // ```
    // Instead, we should store compound-ness as a separate bit from applied/
    // unapplied.
    Bits.UnresolvedMemberExpr.FunctionRefKind =
        static_cast<unsigned>(FunctionRefKind::Unapplied);
  }

  DeclNameRef getName() const { return Name; }
  DeclNameLoc getNameLoc() const { return NameLoc; }
  SourceLoc getDotLoc() const { return DotLoc; }

  SourceLoc getLoc() const { return NameLoc.getBaseNameLoc(); }

  SourceLoc getStartLoc() const { return DotLoc; }
  SourceLoc getEndLoc() const { return NameLoc.getSourceRange().End; }

  /// Retrieve the kind of function reference.
  FunctionRefKind getFunctionRefKind() const {
    return static_cast<FunctionRefKind>(
        Bits.UnresolvedMemberExpr.FunctionRefKind);
  }

  /// Set the kind of function reference.
  void setFunctionRefKind(FunctionRefKind refKind) {
    Bits.UnresolvedMemberExpr.FunctionRefKind = static_cast<unsigned>(refKind);
  }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::UnresolvedMember;
  }
};

/// AnyTryExpr - An abstract superclass for 'try' and 'try!'.
///
/// These are like IdentityExpr in some ways, but they're a bit too
/// semantic differentiated to just always look through.
class AnyTryExpr : public Expr {
  Expr *SubExpr;
  SourceLoc TryLoc;

public:
  AnyTryExpr(ExprKind kind, SourceLoc tryLoc, Expr *sub,
             Type type, bool implicit)
    : Expr(kind, implicit, type), SubExpr(sub), TryLoc(tryLoc) {}

  SourceLoc getLoc() const { return SubExpr->getLoc(); }
  Expr *getSubExpr() const { return SubExpr; }
  void setSubExpr(Expr *E) { SubExpr = E; }

  SourceLoc getTryLoc() const { return TryLoc; }

  SourceLoc getStartLoc() const { return TryLoc; }
  SourceLoc getEndLoc() const { return getSubExpr()->getEndLoc(); }

  static bool classof(const Expr *e) {
    return e->getKind() >= ExprKind::First_AnyTryExpr
        && e->getKind() <= ExprKind::Last_AnyTryExpr;
  }
};

/// TryExpr - A 'try' surrounding an expression, marking that the
/// expression contains code which might throw.
///
/// getSemanticsProvidingExpr() looks through this because it doesn't
/// provide the value and only very specific clients care where the
/// 'try' was written.
class TryExpr : public AnyTryExpr {
public:
  TryExpr(SourceLoc tryLoc, Expr *sub, Type type = Type(),
          bool implicit = false)
    : AnyTryExpr(ExprKind::Try, tryLoc, sub, type, implicit) {}

  static bool classof(const Expr *e) {
    return e->getKind() == ExprKind::Try;
  }
};

/// ForceTryExpr - A 'try!' surrounding an expression, marking that
/// the expression contains code which might throw, but that the code
/// should dynamically assert if it does.
class ForceTryExpr final : public AnyTryExpr {
  SourceLoc ExclaimLoc;

public:
  ForceTryExpr(SourceLoc tryLoc, Expr *sub, SourceLoc exclaimLoc,
               Type type = Type(), bool implicit = false)
    : AnyTryExpr(ExprKind::ForceTry, tryLoc, sub, type, implicit),
      ExclaimLoc(exclaimLoc) {}

  SourceLoc getExclaimLoc() const { return ExclaimLoc; }

  static bool classof(const Expr *e) {
    return e->getKind() == ExprKind::ForceTry;
  }
};

/// A 'try?' surrounding an expression, marking that the expression contains
/// code which might throw, and that the result should be injected into an
/// Optional. If the code does throw, \c nil is produced.
class OptionalTryExpr final : public AnyTryExpr {
  SourceLoc QuestionLoc;

public:
  OptionalTryExpr(SourceLoc tryLoc, Expr *sub, SourceLoc questionLoc,
                  Type type = Type(), bool implicit = false)
    : AnyTryExpr(ExprKind::OptionalTry, tryLoc, sub, type, implicit),
      QuestionLoc(questionLoc) {}

  SourceLoc getQuestionLoc() const { return QuestionLoc; }

  static bool classof(const Expr *e) {
    return e->getKind() == ExprKind::OptionalTry;
  }
};

/// An expression node that does not affect the evaluation of its subexpression.
class IdentityExpr : public Expr {
  Expr *SubExpr;
public:
  IdentityExpr(ExprKind kind,
               Expr *subExpr, Type ty = Type(),
               bool implicit = false)
    : Expr(kind, implicit, ty), SubExpr(subExpr)
  {}
  
  SourceLoc getLoc() const { return SubExpr->getLoc(); }
  Expr *getSubExpr() const { return SubExpr; }
  void setSubExpr(Expr *E) { SubExpr = E; }
  
  static bool classof(const Expr *E) {
    return E->getKind() >= ExprKind::First_IdentityExpr
        && E->getKind() <= ExprKind::Last_IdentityExpr;
  }
};
  
/// The '.self' pseudo-property, which has no effect except to
/// satisfy the syntactic requirement that type values appear only as part of
/// a property chain.
class DotSelfExpr : public IdentityExpr {
  SourceLoc DotLoc;
  SourceLoc SelfLoc;
  
public:
  DotSelfExpr(Expr *subExpr, SourceLoc dot, SourceLoc self,
              Type ty = Type())
    : IdentityExpr(ExprKind::DotSelf, subExpr, ty),
      DotLoc(dot), SelfLoc(self)
  {}
  
  SourceLoc getDotLoc() const { return DotLoc; }
  SourceLoc getSelfLoc() const { return SelfLoc; }

  SourceLoc getStartLoc() const { return getSubExpr()->getStartLoc(); }
  SourceLoc getEndLoc() const { return SelfLoc; }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::DotSelf;
  }
};
  
/// A parenthesized expression like '(x+x)'.  Syntactically,
/// this is just a TupleExpr with exactly one element that has no label.
/// Semantically, however, it serves only as grouping parentheses and
/// does not form an expression of tuple type (unless the sub-expression
/// has tuple type, of course).
class ParenExpr : public IdentityExpr {
  SourceLoc LParenLoc, RParenLoc;
  
public:
  ParenExpr(SourceLoc lploc, Expr *subExpr, SourceLoc rploc,
            bool hasTrailingClosure,
            Type ty = Type())
    : IdentityExpr(ExprKind::Paren, subExpr, ty),
      LParenLoc(lploc), RParenLoc(rploc) {
    Bits.ParenExpr.HasTrailingClosure = hasTrailingClosure;
    assert(lploc.isValid() == rploc.isValid() &&
           "Mismatched source location information");
  }

  SourceLoc getLParenLoc() const { return LParenLoc; }
  SourceLoc getRParenLoc() const { return RParenLoc; }

  // When the locations of the parens are invalid, ask our
  // subexpression for its source range instead.  This isn't a
  // hot path and so we don't both optimizing for it.

  SourceLoc getStartLoc() const {
    return (LParenLoc.isInvalid() ? getSubExpr()->getStartLoc() : LParenLoc);
  }
  SourceLoc getEndLoc() const {
    // If we have a trailing closure, our end point is the end of the
    // trailing closure.
    if (RParenLoc.isInvalid() || Bits.ParenExpr.HasTrailingClosure)
      return getSubExpr()->getEndLoc();
    return RParenLoc;
  }

  /// Whether this expression has a trailing closure as its argument.
  bool hasTrailingClosure() const { return Bits.ParenExpr.HasTrailingClosure; }

  Optional<unsigned>
  getUnlabeledTrailingClosureIndexOfPackedArgument() const {
    return hasTrailingClosure() ? Optional<unsigned>(0) : None;
  }

  static bool classof(const Expr *E) { return E->getKind() == ExprKind::Paren; }
};

/// Represents the result of a chain of accesses or calls hanging off of an
/// \c UnresolvedMemberExpr at the root. This is only used during type checking
/// to give the result type of such a chain representation in the AST. This
/// expression type is always implicit.
class UnresolvedMemberChainResultExpr : public IdentityExpr {
  /// The base of this chain of member accesses.
  UnresolvedMemberExpr *ChainBase;
public:
  UnresolvedMemberChainResultExpr(Expr *subExpr, UnresolvedMemberExpr *base,
                                  Type ty = Type())
    : IdentityExpr(ExprKind::UnresolvedMemberChainResult, subExpr, ty,
                   /*isImplicit=*/true),
      ChainBase(base) {
    assert(base);
  }

  UnresolvedMemberExpr *getChainBase() const { return ChainBase; }

  SWIFT_FORWARD_SOURCE_LOCS_TO(getSubExpr())

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::UnresolvedMemberChainResult;
  }
};
  
/// AwaitExpr - An 'await' surrounding an expression, marking that the
/// expression contains code which is a coroutine that may block.
///
/// getSemanticsProvidingExpr() looks through this because it doesn't
/// provide the value and only very specific clients care where the
/// 'await' was written.
class AwaitExpr final : public IdentityExpr {
  SourceLoc AwaitLoc;
public:
  AwaitExpr(SourceLoc awaitLoc, Expr *sub, Type type = Type(),
            bool implicit = false)
    : IdentityExpr(ExprKind::Await, sub, type, implicit), AwaitLoc(awaitLoc) {
  }
  
  SourceLoc getLoc() const { return AwaitLoc; }
  
  SourceLoc getAwaitLoc() const { return AwaitLoc; }
  SourceLoc getStartLoc() const { return AwaitLoc; }
  SourceLoc getEndLoc() const { return getSubExpr()->getEndLoc(); }

  static bool classof(const Expr *e) {
    return e->getKind() == ExprKind::Await;
  }
};

  
/// TupleExpr - Parenthesized expressions like '(a: x+x)' and '(x, y, 4)'.  Also
/// used to represent the operands to a binary operator.  Note that
/// expressions like '(4)' are represented with a ParenExpr.
class TupleExpr final : public Expr,
    private llvm::TrailingObjects<TupleExpr, Expr *, Identifier, SourceLoc> {
  friend TrailingObjects;

  SourceLoc LParenLoc;
  SourceLoc RParenLoc;

  Optional<unsigned> FirstTrailingArgumentAt;

  size_t numTrailingObjects(OverloadToken<Expr *>) const {
    return getNumElements();
  }
  size_t numTrailingObjects(OverloadToken<Identifier>) const {
    return hasElementNames() ? getNumElements() : 0;
  }
  size_t numTrailingObjects(OverloadToken<SourceLoc>) const {
    return hasElementNames() ? getNumElements() : 0;
  }

  /// Retrieve the buffer containing the element names.
  MutableArrayRef<Identifier> getElementNamesBuffer() {
    if (!hasElementNames())
      return { };

    return { getTrailingObjects<Identifier>(), getNumElements() };
  }

  /// Retrieve the buffer containing the element name locations.
  MutableArrayRef<SourceLoc> getElementNameLocsBuffer() {
    if (!hasElementNameLocs())
      return { };
    
    return { getTrailingObjects<SourceLoc>(), getNumElements() };
  }

  TupleExpr(SourceLoc LParenLoc, SourceLoc RParenLoc,
            ArrayRef<Expr *> SubExprs,
            ArrayRef<Identifier> ElementNames,
            ArrayRef<SourceLoc> ElementNameLocs,
            Optional<unsigned> FirstTrailingArgumentAt, bool Implicit, Type Ty);

public:
  /// Create a tuple.
  static TupleExpr *create(ASTContext &ctx,
                           SourceLoc LParenLoc, 
                           ArrayRef<Expr *> SubExprs,
                           ArrayRef<Identifier> ElementNames, 
                           ArrayRef<SourceLoc> ElementNameLocs,
                           SourceLoc RParenLoc, bool HasTrailingClosure, 
                           bool Implicit, Type Ty = Type());

  static TupleExpr *create(ASTContext &ctx,
                           SourceLoc LParenLoc,
                           SourceLoc RParenLoc,
                           ArrayRef<Expr *> SubExprs,
                           ArrayRef<Identifier> ElementNames,
                           ArrayRef<SourceLoc> ElementNameLocs,
                           Optional<unsigned> FirstTrailingArgumentAt,
                           bool Implicit, Type Ty = Type());

  /// Create an empty tuple.
  static TupleExpr *createEmpty(ASTContext &ctx, SourceLoc LParenLoc, 
                                SourceLoc RParenLoc, bool Implicit);

  /// Create an implicit tuple with no source information.
  static TupleExpr *createImplicit(ASTContext &ctx, ArrayRef<Expr *> SubExprs,
                                   ArrayRef<Identifier> ElementNames);

  SourceLoc getLParenLoc() const { return LParenLoc; }
  SourceLoc getRParenLoc() const { return RParenLoc; }

  SourceRange getSourceRange() const;

  bool hasAnyTrailingClosures() const {
    return (bool) FirstTrailingArgumentAt;
  }

  /// Whether this expression has a trailing closure as its argument.
  bool hasTrailingClosure() const {
    return FirstTrailingArgumentAt
               ? *FirstTrailingArgumentAt == getNumElements() - 1
               : false;
  }

  bool hasMultipleTrailingClosures() const {
    return FirstTrailingArgumentAt ? !hasTrailingClosure() : false;
  }

  Optional<unsigned>
  getUnlabeledTrailingClosureIndexOfPackedArgument() const {
    return FirstTrailingArgumentAt;
  }

  /// Retrieve the elements of this tuple.
  MutableArrayRef<Expr*> getElements() {
    return { getTrailingObjects<Expr *>(), getNumElements() };
  }

  /// Retrieve the elements of this tuple.
  ArrayRef<Expr*> getElements() const {
    return { getTrailingObjects<Expr *>(), getNumElements() };
  }

  MutableArrayRef<Expr*> getTrailingElements() {
    return getElements().take_back(getNumTrailingElements());
  }
  
  ArrayRef<Expr*> getTrailingElements() const {
    return getElements().take_back(getNumTrailingElements());
  }
  
  unsigned getNumElements() const { return Bits.TupleExpr.NumElements; }

  unsigned getNumTrailingElements() const {
    return FirstTrailingArgumentAt
               ? getNumElements() - *FirstTrailingArgumentAt
               : 0;
  }
  
  Expr *getElement(unsigned i) const {
    return getElements()[i];
  }
  void setElement(unsigned i, Expr *e) {
    getElements()[i] = e;
  }

  /// Whether this tuple has element names.
  bool hasElementNames() const { 
    return Bits.TupleExpr.HasElementNames;
  }

  /// Retrieve the element names for a tuple.
  ArrayRef<Identifier> getElementNames() const { 
    return const_cast<TupleExpr *>(this)->getElementNamesBuffer();
  }
  
  /// Retrieve the ith element name.
  Identifier getElementName(unsigned i) const {
    return hasElementNames() ? getElementNames()[i] : Identifier();
  }
  
  /// Whether this tuple has element name locations.
  bool hasElementNameLocs() const { 
    return Bits.TupleExpr.HasElementNameLocations;
  }

  /// Retrieve the locations of the element names for a tuple.
  ArrayRef<SourceLoc> getElementNameLocs() const {
    return const_cast<TupleExpr *>(this)->getElementNameLocsBuffer();
  }

  /// Retrieve the location of the ith label, if known.
  SourceLoc getElementNameLoc(unsigned i) const {
    if (hasElementNameLocs())
      return getElementNameLocs()[i];
    
    return SourceLoc();
  }

  static bool classof(const Expr *E) { return E->getKind() == ExprKind::Tuple; }
};

/// A collection literal expression.
///
/// The subexpression is represented as a TupleExpr or ParenExpr and
/// passed on to the appropriate semantics-providing conversion
/// operation.
class CollectionExpr : public Expr {
  SourceLoc LBracketLoc;
  SourceLoc RBracketLoc;
  ConcreteDeclRef Initializer;

  /// Retrieve the intrusive pointer storage from the subtype
  Expr *const *getTrailingObjectsPointer() const;
  Expr **getTrailingObjectsPointer() {
    const CollectionExpr *temp = this;
    return const_cast<Expr**>(temp->getTrailingObjectsPointer());
  }

  /// Retrieve the intrusive pointer storage from the subtype
  const SourceLoc *getTrailingSourceLocs() const;
  SourceLoc *getTrailingSourceLocs() {
    const CollectionExpr *temp = this;
    return const_cast<SourceLoc*>(temp->getTrailingSourceLocs());
  }

protected:
  CollectionExpr(ExprKind Kind, SourceLoc LBracketLoc,
                 ArrayRef<Expr*> Elements, ArrayRef<SourceLoc> CommaLocs,
                 SourceLoc RBracketLoc, Type Ty)
    : Expr(Kind, /*Implicit=*/false, Ty),
      LBracketLoc(LBracketLoc), RBracketLoc(RBracketLoc) {
    Bits.CollectionExpr.IsTypeDefaulted = false;
    Bits.CollectionExpr.NumSubExprs = Elements.size();
    Bits.CollectionExpr.NumCommas = CommaLocs.size();
    assert(Bits.CollectionExpr.NumCommas == CommaLocs.size() && "Truncation");
    std::uninitialized_copy(Elements.begin(), Elements.end(),
                            getTrailingObjectsPointer());
    std::uninitialized_copy(CommaLocs.begin(), CommaLocs.end(),
                            getTrailingSourceLocs());
  }

public:

  /// Retrieve the elements stored in the collection.
  ArrayRef<Expr *> getElements() const {
    return {getTrailingObjectsPointer(), Bits.CollectionExpr.NumSubExprs};
  }
  MutableArrayRef<Expr *> getElements() {
    return {getTrailingObjectsPointer(), Bits.CollectionExpr.NumSubExprs};
  }
  Expr *getElement(unsigned i) const { return getElements()[i]; }
  void setElement(unsigned i, Expr *E) { getElements()[i] = E; }
  unsigned getNumElements() const { return Bits.CollectionExpr.NumSubExprs; }

  /// Retrieve the comma source locations stored in the collection. Please note
  /// that trailing commas are currently allowed, and that invalid code may have
  /// stray or missing commas.
  MutableArrayRef<SourceLoc> getCommaLocs() {
    return {getTrailingSourceLocs(), static_cast<size_t>(Bits.CollectionExpr.NumCommas)};
  }
  ArrayRef<SourceLoc> getCommaLocs() const {
    return {getTrailingSourceLocs(), static_cast<size_t>(Bits.CollectionExpr.NumCommas)};
  }
  unsigned getNumCommas() const { return Bits.CollectionExpr.NumCommas; }

  bool isTypeDefaulted() const { return Bits.CollectionExpr.IsTypeDefaulted; }
  void setIsTypeDefaulted(bool value = true) {
    Bits.CollectionExpr.IsTypeDefaulted = value;
  }

  SourceLoc getLBracketLoc() const { return LBracketLoc; }
  SourceLoc getRBracketLoc() const { return RBracketLoc; }
  SourceRange getSourceRange() const {
    return SourceRange(LBracketLoc, RBracketLoc);
  }

  static bool classof(const Expr *e) {
    return e->getKind() >= ExprKind::First_CollectionExpr &&
           e->getKind() <= ExprKind::Last_CollectionExpr;
  }

  /// Retrieve the initializer that will be used to construct the 'array'
  /// literal from the result of the initializer.
  ConcreteDeclRef getInitializer() const { return Initializer; }

  /// Set the initializer that will be used to construct the 'array' literal.
  void setInitializer(ConcreteDeclRef initializer) {
    Initializer = initializer;
  }
};
 
/// An array literal expression [a, b, c].
class ArrayExpr final : public CollectionExpr,
    private llvm::TrailingObjects<ArrayExpr, Expr*, SourceLoc> {
  friend TrailingObjects;
  friend CollectionExpr;

  size_t numTrailingObjects(OverloadToken<Expr *>) const {
    return getNumElements();
  }
  size_t numTrailingObjects(OverloadToken<SourceLoc>) const {
    return getNumCommas();
  }

  ArrayExpr(SourceLoc LBracketLoc, ArrayRef<Expr*> Elements,
            ArrayRef<SourceLoc> CommaLocs,
            SourceLoc RBracketLoc, Type Ty)
  : CollectionExpr(ExprKind::Array, LBracketLoc, Elements, CommaLocs,
                   RBracketLoc, Ty) { }
public:
  static ArrayExpr *create(ASTContext &C, SourceLoc LBracketLoc,
                           ArrayRef<Expr*> Elements,
                           ArrayRef<SourceLoc> CommaLocs,
                           SourceLoc RBracketLoc,
                           Type Ty = Type());

  static bool classof(const Expr *e) {
    return e->getKind() == ExprKind::Array;
  }

  Type getElementType();
};

/// A dictionary literal expression [a : x, b : y, c : z].
class DictionaryExpr final : public CollectionExpr,
    private llvm::TrailingObjects<DictionaryExpr, Expr*, SourceLoc> {
  friend TrailingObjects;
  friend CollectionExpr;

  size_t numTrailingObjects(OverloadToken<Expr *>) const {
    return getNumElements();
  }
  size_t numTrailingObjects(OverloadToken<SourceLoc>) const {
    return getNumCommas();
  }

  DictionaryExpr(SourceLoc LBracketLoc, ArrayRef<Expr*> Elements,
                 ArrayRef<SourceLoc> CommaLocs,
                 SourceLoc RBracketLoc, Type Ty)
    : CollectionExpr(ExprKind::Dictionary, LBracketLoc, Elements, CommaLocs,
                     RBracketLoc, Ty) { }
public:

  static DictionaryExpr *create(ASTContext &C, SourceLoc LBracketLoc,
                                ArrayRef<Expr*> Elements,
                                ArrayRef<SourceLoc> CommaLocs,
                                SourceLoc RBracketLoc,
                                Type Ty = Type());

  static bool classof(const Expr *e) {
    return e->getKind() == ExprKind::Dictionary;
  }

  Type getElementType();
};

/// Subscripting expressions like a[i] that refer to an element within a
/// container.
///
/// There is no built-in subscripting in the language. Rather, a fully
/// type-checked and well-formed subscript expression refers to a subscript
/// declaration, which provides a getter and (optionally) a setter that will
/// be used to perform reads/writes.
class SubscriptExpr final : public LookupExpr,
                            public TrailingCallArguments<SubscriptExpr> {
  friend TrailingCallArguments;

  Expr *Index;

  SubscriptExpr(Expr *base, Expr *index, ArrayRef<Identifier> argLabels,
                ArrayRef<SourceLoc> argLabelLocs, bool hasTrailingClosure,
                ConcreteDeclRef decl, bool implicit, AccessSemantics semantics);
  
public:
  /// Create a subscript.
  ///
  /// Note: do not create new callers to this entry point; use the entry point
  /// that takes separate index arguments.
  static SubscriptExpr *create(
      ASTContext &ctx, Expr *base, Expr *index,
      ConcreteDeclRef decl = ConcreteDeclRef(), bool implicit = false,
      AccessSemantics semantics = AccessSemantics::Ordinary,
      llvm::function_ref<Type(Expr *)> getType = [](Expr *E) -> Type {
        return E->getType();
      });

  /// Create a new subscript.
  static SubscriptExpr *create(ASTContext &ctx, Expr *base,
                               SourceLoc lSquareLoc,
                               ArrayRef<Expr *> indexArgs,
                               ArrayRef<Identifier> indexArgLabels,
                               ArrayRef<SourceLoc> indexArgLabelLocs,
                               SourceLoc rSquareLoc,
                               ArrayRef<TrailingClosure> trailingClosures,
                               ConcreteDeclRef decl = ConcreteDeclRef(),
                               bool implicit = false,
                               AccessSemantics semantics
                                 = AccessSemantics::Ordinary);

  /// getIndex - Retrieve the index of the subscript expression, i.e., the
  /// "offset" into the base value.
  Expr *getIndex() const { return Index; }
  void setIndex(Expr *E) { Index = E; }

  unsigned getNumArguments() const {
    return Bits.SubscriptExpr.NumArgLabels;
  }

  bool hasArgumentLabelLocs() const {
    return Bits.SubscriptExpr.HasArgLabelLocs;
  }

  /// Whether this call was written with a trailing closure.
  bool hasTrailingClosure() const {
    return Bits.SubscriptExpr.HasTrailingClosure;
  }

  /// Return the index of the unlabeled trailing closure argument.
  Optional<unsigned> getUnlabeledTrailingClosureIndex() const {
    return getIndex()->getUnlabeledTrailingClosureIndexOfPackedArgument();
  }

  /// Determine whether this subscript reference should bypass the
  /// ordinary accessors.
  AccessSemantics getAccessSemantics() const {
    return (AccessSemantics) Bits.SubscriptExpr.Semantics;
  }
  
  SourceLoc getLoc() const { return Index->getStartLoc(); }
  SourceLoc getStartLoc() const { return getBase()->getStartLoc(); }
  SourceLoc getEndLoc() const {
    auto end = Index->getEndLoc();
    return end.isValid() ? end : getBase()->getEndLoc();
  }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::Subscript;
  }
};

/// Subscripting expression that applies a keypath to a base.
class KeyPathApplicationExpr : public Expr {
  Expr *Base;
  Expr *KeyPath;
  SourceLoc LBracketLoc, RBracketLoc;
  
public:
  KeyPathApplicationExpr(Expr *base, SourceLoc lBracket, Expr *keyPath,
                         SourceLoc rBracket, Type ty, bool implicit)
    : Expr(ExprKind::KeyPathApplication, implicit, ty),
      Base(base), KeyPath(keyPath), LBracketLoc(lBracket), RBracketLoc(rBracket)
  {}
  
  SourceLoc getLoc() const { return LBracketLoc; }
  SourceLoc getStartLoc() const { return Base->getStartLoc(); }
  SourceLoc getEndLoc() const { return RBracketLoc; }
  
  Expr *getBase() const { return Base; }
  void setBase(Expr *E) { Base = E; }
  Expr *getKeyPath() const { return KeyPath; }
  void setKeyPath(Expr *E) { KeyPath = E; }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::KeyPathApplication;
  }
};

/// A member access (foo.bar) on an expression with unresolved type.
class UnresolvedDotExpr : public Expr {
  Expr *SubExpr;
  SourceLoc DotLoc;
  DeclNameLoc NameLoc;
  DeclNameRef Name;
  ArrayRef<ValueDecl *> OuterAlternatives;

public:
  UnresolvedDotExpr(
      Expr *subexpr, SourceLoc dotloc, DeclNameRef name, DeclNameLoc nameloc,
      bool Implicit,
      ArrayRef<ValueDecl *> outerAlternatives = ArrayRef<ValueDecl *>())
      : Expr(ExprKind::UnresolvedDot, Implicit), SubExpr(subexpr),
        DotLoc(dotloc), NameLoc(nameloc), Name(name),
        OuterAlternatives(outerAlternatives) {
    Bits.UnresolvedDotExpr.FunctionRefKind =
      static_cast<unsigned>(NameLoc.isCompound() ? FunctionRefKind::Compound
                                                 : FunctionRefKind::Unapplied);
  }

  static UnresolvedDotExpr *createImplicit(
      ASTContext &C, Expr *base, DeclName name) {
    return new (C) UnresolvedDotExpr(base, SourceLoc(),
                                     DeclNameRef(name), DeclNameLoc(),
                                     /*implicit=*/true);
  }

  static UnresolvedDotExpr *createImplicit(
      ASTContext &C, Expr *base,
      DeclBaseName baseName, ArrayRef<Identifier> argLabels) {
    return UnresolvedDotExpr::createImplicit(C, base,
                                             DeclName(C, baseName, argLabels));
  }

  static UnresolvedDotExpr *createImplicit(
      ASTContext &C, Expr *base,
      DeclBaseName baseName, ParameterList *paramList) {
    return UnresolvedDotExpr::createImplicit(C, base,
                                             DeclName(C, baseName, paramList));
  }

  SourceLoc getLoc() const {
    if (NameLoc.isValid())
      return NameLoc.getBaseNameLoc();
    else if (DotLoc.isValid())
      return DotLoc;
    else
      return SubExpr->getEndLoc();
  }

  SourceLoc getStartLoc() const {
    auto SubLoc = SubExpr->getStartLoc();
    if (SubLoc.isValid())
      return SubLoc;
    else if (DotLoc.isValid())
      return DotLoc;
    else
      return NameLoc.getSourceRange().Start;
  }
  SourceLoc getEndLoc() const {
    if (NameLoc.isValid())
      return NameLoc.getSourceRange().End;
    else if (DotLoc.isValid())
      return DotLoc;
    else
      return SubExpr->getEndLoc();
  }

  SourceLoc getDotLoc() const { return DotLoc; }
  Expr *getBase() const { return SubExpr; }
  void setBase(Expr *e) { SubExpr = e; }

  DeclNameRef getName() const { return Name; }
  DeclNameLoc getNameLoc() const { return NameLoc; }

  ArrayRef<ValueDecl *> getOuterAlternatives() const {
    return OuterAlternatives;
  }

  /// Retrieve the kind of function reference.
  FunctionRefKind getFunctionRefKind() const {
    return static_cast<FunctionRefKind>(Bits.UnresolvedDotExpr.FunctionRefKind);
  }

  /// Set the kind of function reference.
  void setFunctionRefKind(FunctionRefKind refKind) {
    Bits.UnresolvedDotExpr.FunctionRefKind = static_cast<unsigned>(refKind);
  }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::UnresolvedDot;
  }
};

/// TupleElementExpr - Refer to an element of a tuple,
/// e.g. "(1,field:2).field".
class TupleElementExpr : public Expr {
  Expr *SubExpr;
  SourceLoc NameLoc;
  SourceLoc DotLoc;

public:
  TupleElementExpr(Expr *SubExpr, SourceLoc DotLoc, unsigned FieldNo,
                   SourceLoc NameLoc, Type Ty)
    : Expr(ExprKind::TupleElement, /*Implicit=*/false, Ty), SubExpr(SubExpr),
      NameLoc(NameLoc), DotLoc(DotLoc) {
    Bits.TupleElementExpr.FieldNo = FieldNo;
  }

  SourceLoc getLoc() const { return NameLoc; }
  Expr *getBase() const { return SubExpr; }
  void setBase(Expr *e) { SubExpr = e; }

  unsigned getFieldNumber() const { return Bits.TupleElementExpr.FieldNo; }
  SourceLoc getNameLoc() const { return NameLoc; }  
  SourceLoc getDotLoc() const { return DotLoc; }
  
  SourceLoc getStartLoc() const { return getBase()->getStartLoc(); }
  SourceLoc getEndLoc() const { return getNameLoc(); }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::TupleElement;
  }
};

/// Describes a monadic bind from T? to T.
///
/// In a ?-chain expression, this is the part that's spelled with a
/// postfix ?.
///
/// A BindOptionalExpr must always appear within a
/// OptionalEvaluationExpr.  If the operand of the BindOptionalExpr
/// evaluates to a missing value, the OptionalEvaluationExpr
/// immediately completes and produces a missing value in the result
/// type.
///
/// The depth of the BindOptionalExpr indicates which
/// OptionalEvaluationExpr is completed, in case the BindOptionalExpr
/// is contained within more than one such expression.
class BindOptionalExpr : public Expr {
  Expr *SubExpr;
  SourceLoc QuestionLoc;

public:
  BindOptionalExpr(Expr *subExpr, SourceLoc questionLoc,
                   unsigned depth, Type ty = Type())
    : Expr(ExprKind::BindOptional, /*Implicit=*/ questionLoc.isInvalid(), ty),
      SubExpr(subExpr), QuestionLoc(questionLoc) {
    Bits.BindOptionalExpr.Depth = depth;
    assert(Bits.BindOptionalExpr.Depth == depth && "bitfield truncation");
  }

  SourceRange getSourceRange() const {
    if (QuestionLoc.isInvalid())
      return SubExpr->getSourceRange();
    return SourceRange(SubExpr->getStartLoc(), QuestionLoc);
  }
  SourceLoc getStartLoc() const {
    return SubExpr->getStartLoc();
  }
  SourceLoc getEndLoc() const {
    return (QuestionLoc.isInvalid() ? SubExpr->getEndLoc() : QuestionLoc);
  }
  SourceLoc getLoc() const { 
    if (isImplicit())
      return SubExpr->getLoc();

    return getQuestionLoc(); 
  }
  SourceLoc getQuestionLoc() const { return QuestionLoc; }

  unsigned getDepth() const { return Bits.BindOptionalExpr.Depth; }
  void setDepth(unsigned depth) {
    Bits.BindOptionalExpr.Depth = depth;
  }

  Expr *getSubExpr() const { return SubExpr; }
  void setSubExpr(Expr *expr) { SubExpr = expr; }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::BindOptional;
  }
};

/// Describes the outer limits of an operation containing
/// monadic binds of T? to T.
///
/// In a ?-chain expression, this is implicitly formed at the outer
/// limits of the chain.  For example, in (foo?.bar?().baz).fred,
/// this is nested immediately within the parens.
///
/// This expression will always have optional type.
class OptionalEvaluationExpr : public Expr {
  Expr *SubExpr;

public:
  OptionalEvaluationExpr(Expr *subExpr, Type ty = Type())
    : Expr(ExprKind::OptionalEvaluation, /*Implicit=*/ true, ty),
      SubExpr(subExpr) {}

  SWIFT_FORWARD_SOURCE_LOCS_TO(SubExpr)

  Expr *getSubExpr() const { return SubExpr; }
  void setSubExpr(Expr *expr) { SubExpr = expr; }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::OptionalEvaluation;
  }
};

/// An expression that forces an optional to its underlying value.
///
/// \code
/// func parseInt(s : String) -> Int? { ... }
///
/// var maybeInt = parseInt("5")     // returns an Int?
/// var forcedInt = parseInt("5")!   // returns an Int; fails on empty optional
/// \endcode
///
class ForceValueExpr : public Expr {
  Expr *SubExpr;
  SourceLoc ExclaimLoc;

public:
  ForceValueExpr(Expr *subExpr, SourceLoc exclaimLoc, bool forcedIUO = false)
    : Expr(ExprKind::ForceValue, /*Implicit=*/exclaimLoc.isInvalid(), Type()),
      SubExpr(subExpr), ExclaimLoc(exclaimLoc) {
    Bits.ForceValueExpr.ForcedIUO = forcedIUO;
  }

  SourceRange getSourceRange() const {
    if (ExclaimLoc.isInvalid())
      return SubExpr->getSourceRange();

    return SourceRange(SubExpr->getStartLoc(), ExclaimLoc);
  }
  SourceLoc getStartLoc() const {
    return SubExpr->getStartLoc();
  }
  SourceLoc getEndLoc() const {
    return (isImplicit() ? SubExpr->getEndLoc() : getExclaimLoc());
  }
  SourceLoc getLoc() const {
    if (!isImplicit())
      return getExclaimLoc();
    
    return SubExpr->getLoc();
  }
  SourceLoc getExclaimLoc() const { return ExclaimLoc; }

  Expr *getSubExpr() const { return SubExpr; }
  void setSubExpr(Expr *expr) { SubExpr = expr; }

  bool isForceOfImplicitlyUnwrappedOptional() const {
    return Bits.ForceValueExpr.ForcedIUO;
  }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::ForceValue;
  }
};

/// An expression that grants temporary escapability to a nonescaping
/// closure value.
///
/// This expression is formed by the type checker when a call to the
/// `withoutActuallyEscaping` declaration is made.
class MakeTemporarilyEscapableExpr : public Expr {
  Expr *NonescapingClosureValue;
  OpaqueValueExpr *EscapingClosureValue;
  Expr *SubExpr;
  SourceLoc NameLoc, LParenLoc, RParenLoc;
  Expr *OriginalExpr;

public:
  MakeTemporarilyEscapableExpr(SourceLoc NameLoc,
                               SourceLoc LParenLoc,
                               Expr *NonescapingClosureValue,
                               Expr *SubExpr,
                               SourceLoc RParenLoc,
                               OpaqueValueExpr *OpaqueValueForEscapingClosure,
                               Expr *OriginalExpr,
                               bool implicit = false)
    : Expr(ExprKind::MakeTemporarilyEscapable, implicit, Type()),
      NonescapingClosureValue(NonescapingClosureValue),
      EscapingClosureValue(OpaqueValueForEscapingClosure),
      SubExpr(SubExpr),
      NameLoc(NameLoc), LParenLoc(LParenLoc), RParenLoc(RParenLoc),
      OriginalExpr(OriginalExpr)
  {}
  
  SourceLoc getStartLoc() const {
    return NameLoc;
  }
  SourceLoc getEndLoc() const {
    return RParenLoc;
  }
  
  SourceLoc getLoc() const {
    return NameLoc;
  }
  
  /// Retrieve the opaque value representing the escapable copy of the
  /// closure.
  OpaqueValueExpr *getOpaqueValue() const { return EscapingClosureValue; }
  
  /// Retrieve the nonescaping closure expression.
  Expr *getNonescapingClosureValue() const {
    return NonescapingClosureValue;
  }
  void setNonescapingClosureValue(Expr *e) {
    NonescapingClosureValue = e;
  }
  
  /// Retrieve the subexpression that has access to the escapable copy of the
  /// closure.
  Expr *getSubExpr() const {
    return SubExpr;
  }
  void setSubExpr(Expr *e) {
    SubExpr = e;
  }

  /// Retrieve the original 'withoutActuallyEscaping(closure) { ... }'
  //  expression.
  Expr *getOriginalExpr() const {
    return OriginalExpr;
  }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::MakeTemporarilyEscapable;
  }
};

/// An expression that opens up a value of protocol or protocol
/// composition type and gives a name to its dynamic type.
///
/// This expression is implicitly created by the type checker when
/// calling a method on a protocol. In the future, this may become an
/// actual operation within the language.
class OpenExistentialExpr : public Expr {
  Expr *ExistentialValue;
  OpaqueValueExpr *OpaqueValue;
  Expr *SubExpr;
  SourceLoc ExclaimLoc;

public:
  OpenExistentialExpr(Expr *existentialValue,
                      OpaqueValueExpr *opaqueValue,
                      Expr *subExpr,
                      Type subExprTy)
    : Expr(ExprKind::OpenExistential, /*Implicit=*/ true, subExprTy),
      ExistentialValue(existentialValue), OpaqueValue(opaqueValue), 
      SubExpr(subExpr) { }

  SWIFT_FORWARD_SOURCE_LOCS_TO(SubExpr)

  /// Retrieve the expression that is being evaluated using the
  /// archetype value.
  ///
  /// This subexpression (and no other) may refer to the archetype
  /// type or the opaque value that stores the archetype's value.
  Expr *getSubExpr() const { return SubExpr; }

  /// Set the subexpression that is being evaluated.
  void setSubExpr(Expr *expr) { SubExpr = expr; }

  /// Retrieve the existential value that is being opened.
  Expr *getExistentialValue() const { return ExistentialValue; }

  /// Set the existential val ue that is being opened.
  void setExistentialValue(Expr *expr) { ExistentialValue = expr; }

  /// Retrieve the opaque value representing the value (of archetype
  /// type) stored in the existential.
  OpaqueValueExpr *getOpaqueValue() const { return OpaqueValue; }

  /// Retrieve the opened archetype, which can only be referenced
  /// within this expression's subexpression.
  OpenedArchetypeType *getOpenedArchetype() const;

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::OpenExistential;
  }
};

/// ImplicitConversionExpr - An abstract class for expressions which
/// implicitly convert the value of an expression in some way.
class ImplicitConversionExpr : public Expr {
  Expr *SubExpr;

protected:
  ImplicitConversionExpr(ExprKind kind, Expr *subExpr, Type ty)
    : Expr(kind, /*Implicit=*/true, ty), SubExpr(subExpr) {}

public:
  SWIFT_FORWARD_SOURCE_LOCS_TO(SubExpr)

  Expr *getSubExpr() const { return SubExpr; }
  void setSubExpr(Expr *e) { SubExpr = e; }

  Expr *getSyntacticSubExpr() const {
    if (auto *ICE = dyn_cast<ImplicitConversionExpr>(SubExpr))
      return ICE->getSyntacticSubExpr();
    return SubExpr;
  }

  static bool classof(const Expr *E) {
    return E->getKind() >= ExprKind::First_ImplicitConversionExpr &&
           E->getKind() <= ExprKind::Last_ImplicitConversionExpr;
  }
};

/// The implicit conversion from a class metatype to AnyObject.
class ClassMetatypeToObjectExpr : public ImplicitConversionExpr {
public:
  ClassMetatypeToObjectExpr(Expr *subExpr, Type ty)