blob: 74800cb8e3e73f34aedd585a20c869498c2b3515 [file] [log] [blame]
.. _ABI:
.. highlight:: none
mangled-name ::= '$s' global // Swift stable mangling
mangled-name ::= '_T0' global // Swift 4.0
mangled-name ::= '$S' global // Swift 4.2
All Swift-mangled names begin with a common prefix. Since Swift 4.0, the
compiler has used variations of the mangling described in this document, though
pre-stable versions may not exactly conform to this description. By using
distinct prefixes, tools can attempt to accommodate bugs and version variations
in pre-stable versions of Swift.
The basic mangling scheme is a list of 'operators' where the operators are
structured in a post-fix order. For example the mangling may start with an
identifier but only later in the mangling a type-like operator defines how this
identifier has to be interpreted::
4Test3FooC // The trailing 'C' says that 'Foo' is a class in module 'Test'
Operators are either identifiers or a sequence of one or more characters,
like ``C`` for class.
All operators share the same name-space. Important operators are a single
character, which means that no other operator may start with the same
Some less important operators are longer and may also contain one or more
natural numbers. But it's always important that the demangler can identify the
end (the last character) of an operator. For example, it's not possible to
determine the last character if there are two operators ``M`` and ``Ma``:
``a`` could belong to ``M`` or it could be the first character of the next
The intention of the post-fix order is to optimize for common pre-fixes.
Regardless, if it's the mangling for a metatype or a function in a module, the
mangled name will start with the module name (after the ``_S``).
In the following, productions which are only _part_ of an operator, are
named with uppercase letters.
Symbolic references
The Swift compiler emits mangled names into binary images to encode
references to types for runtime instantiation and reflection. In a binary,
these mangled names may embed pointers to runtime data
structures in order to more efficiently represent locally-defined types.
We call these pointers **symbolic references**.
These references will be introduced by a control character in the range
`\x01` ... `\x1F`, which indicates the kind of symbolic reference, followed by
some number of arbitrary bytes *which may include null bytes*. Code that
processes mangled names out of Swift binaries needs to be aware of symbolic
references in order to properly terminate strings; a null terminator may be
part of a symbolic reference.
symbolic-reference ::= [\x01-\x17] .{4} // Relative symbolic reference
#if sizeof(void*) == 8
symbolic-reference ::= [\x18-\x1F] .{8} // Absolute symbolic reference
#elif sizeof(void*) == 4
symbolic-reference ::= [\x18-\x1F] .{4} // Absolute symbolic reference
Symbolic references are only valid in compiler-emitted metadata structures
and must only appear in read-only parts of a binary image. APIs and tools
that interpret Swift mangled names from potentially uncontrolled inputs must
refuse to interpret symbolic references.
The following symbolic reference kinds are currently implemented:
{any-generic-type, protocol} ::= '\x01' .{4} // Reference points directly to context descriptor
{any-generic-type, protocol} ::= '\x02' .{4} // Reference points indirectly to context descriptor
{any-generic-type, protocol, opaque-type-decl-name} ::= '\x01' .{4} // Reference points directly to context descriptor
{any-generic-type, protocol, opaque-type-decl-name} ::= '\x02' .{4} // Reference points indirectly to context descriptor
// The grammatical role of the symbolic reference is determined by the
// kind of context descriptor referenced
protocol-conformance-ref ::= '\x03' .{4} // Reference points directly to protocol conformance descriptor (NOT IMPLEMENTED)
protocol-conformance-ref ::= '\x04' .{4} // Reference points indirectly to protocol conformance descriptor (NOT IMPLEMENTED)
dependent-associated-conformance ::= '\x05' .{4} // Reference points directly to associated conformance descriptor (NOT IMPLEMENTED)
dependent-associated-conformance ::= '\x06' .{4} // Reference points indirectly to associated conformance descriptor (NOT IMPLEMENTED)
associated-conformance-access-function ::= '\x07' .{4} // Reference points directly to associated conformance access function relative to the protocol
associated-conformance-access-function ::= '\x08' .{4} // Reference points directly to associated conformance access function relative to the conforming type
// keypaths only in Swift 5.0, generalized in Swift 5.1
metadata-access-function ::= '\x09' .{4} // Reference points directly to metadata access function that can be invoked to produce referenced object
A mangled name may also include ``\xFF`` bytes, which are only used for
alignment padding. They do not affect what the mangled name references and can
be skipped over and ignored.
global ::= type 'N' // type metadata (address point)
// -- type starts with [BCOSTV]
global ::= type 'Mf' // 'full' type metadata (start of object)
global ::= type 'MP' // type metadata pattern
global ::= type 'Ma' // type metadata access function
global ::= type 'ML' // type metadata lazy cache variable
global ::= nominal-type 'Mr' // generic type completion function
global ::= nominal-type 'Mi' // generic type instantiation function
global ::= nominal-type 'MI' // generic type instantiation cache
global ::= nominal-type 'Ml' // in-place type initialization cache
global ::= nominal-type 'Mm' // class metaclass
global ::= nominal-type 'Mn' // nominal type descriptor
global ::= opaque-type-decl-name 'MQ' // opaque type descriptor -- added in Swift 5.1
global ::= nominal-type 'Mu' // class method lookup function
global ::= nominal-type 'MU' // ObjC metadata update callback function
global ::= nominal-type 'Ms' // ObjC resilient class stub
global ::= nominal-type 'Mt' // Full ObjC resilient class stub (private)
global ::= module 'MXM' // module descriptor
global ::= context 'MXE' // extension descriptor
global ::= context 'MXX' // anonymous context descriptor
global ::= context identifier 'MXY' // anonymous context descriptor
global ::= type assoc-type-list 'MXA' // generic parameter ref (HISTORICAL)
global ::= protocol 'Mp' // protocol descriptor
global ::= nominal-type 'Mo' // class metadata immediate member base offset
global ::= type 'MF' // metadata for remote mirrors: field descriptor
global ::= type 'MB' // metadata for remote mirrors: builtin type descriptor
global ::= protocol-conformance 'MA' // metadata for remote mirrors: associated type descriptor
global ::= nominal-type 'MC' // metadata for remote mirrors: superclass descriptor
// TODO check this::
global ::= mangled-name 'TA' // partial application forwarder
global ::= mangled-name 'Ta' // ObjC partial application forwarder
global ::= type 'w' VALUE-WITNESS-KIND // value witness
global ::= protocol 'MS' // protocol self-conformance descriptor
global ::= protocol 'WS' // protocol self-conformance witness table
global ::= protocol-conformance 'Mc' // protocol conformance descriptor
global ::= protocol-conformance 'WP' // protocol witness table
global ::= protocol-conformance 'Wa' // protocol witness table accessor (HISTORICAL)
global ::= protocol-conformance 'WG' // generic protocol witness table (HISTORICAL)
global ::= protocol-conformance 'Wp' // protocol witness table pattern
global ::= protocol-conformance 'Wr' // resilient witness table (HISTORICAL)
global ::= protocol-conformance 'WI' // generic protocol witness table instantiation function
global ::= type protocol-conformance 'WL' // lazy protocol witness table cache variable
global ::= protocol-conformance identifier 'Wt' // associated type metadata accessor (HISTORICAL)
global ::= protocol-conformance assoc-type-list protocol 'WT' // associated type witness table accessor
global ::= protocol-conformance protocol 'Wb' // base protocol witness table accessor
global ::= type protocol-conformance 'Wl' // lazy protocol witness table accessor
global ::= type 'WV' // value witness table
global ::= entity 'Wvd' // field offset
global ::= entity 'WC' // resilient enum tag index
global ::= global 'MK' // instantiation cache associated with global
global ::= global 'MJ' // noncanonical specialized generic type metadata instantiation cache associated with global
global ::= global 'MN' // noncanonical specialized generic type metadata for global
global ::= global 'Mz' // canonical specialized generic type metadata caching token
global ::= context (decl-name '_')+ 'WZ' // global variable one-time initialization function
global ::= context (decl-name '_')+ 'Wz' // global variable one-time initialization token
A direct symbol resolves directly to the address of an object. An
indirect symbol resolves to the address of a pointer to the object.
They are distinct manglings to make a certain class of bugs
immediately obvious.
The terminology is slightly overloaded when discussing offsets. A
direct offset resolves to a variable holding the true offset. An
indirect offset resolves to a variable holding an offset to be applied
to type metadata to get the address of the true offset. (Offset
variables are required when the object being accessed lies within a
resilient structure. When the layout of the object may depend on
generic arguments, these offsets must be kept in metadata. Indirect
field offsets are therefore required when accessing fields in generic
types where the metadata itself has unknown layout.)
global ::= global 'Tj' // resilient method dispatch thunk
global ::= global 'Tq' // method descriptor
global ::= global 'TO' // ObjC-as-swift thunk
global ::= global 'To' // swift-as-ObjC thunk
global ::= global 'TD' // dynamic dispatch thunk
global ::= global 'Td' // direct method reference thunk
global ::= global 'TI' // implementation of a dynamic_replaceable function
global :== global 'Tu' // async function pointer of a function
global ::= global 'TX' // function pointer of a dynamic_replaceable function
global ::= entity entity 'TV' // vtable override thunk, derived followed by base
global ::= type label-list? 'D' // type mangling for the debugger with label list for function types.
global ::= type 'TC' // continuation prototype (not actually used for real symbols)
global ::= protocol-conformance entity 'TW' // protocol witness thunk
global ::= entity 'TS' // protocol self-conformance witness thunk
global ::= context identifier identifier 'TB' // property behavior initializer thunk (not used currently)
global ::= context identifier identifier 'Tb' // property behavior setter thunk (not used currently)
global ::= global specialization // function specialization
global ::= global 'Tm' // merged function
global ::= entity // some identifiable thing
global ::= from-type to-type generic-signature? 'TR' // reabstraction thunk
global ::= from-type to-type generic-signature? 'TR' // reabstraction thunk
global ::= impl-function-type type 'Tz' // objc-to-swift-async completion handler block implementation
global ::= impl-function-type type 'TZ' // objc-to-swift-async completion handler block implementation (predefined by runtime)
global ::= from-type to-type self-type generic-signature? 'Ty' // reabstraction thunk with dynamic 'Self' capture
global ::= from-type to-type generic-signature? 'Tr' // obsolete mangling for reabstraction thunk
global ::= entity generic-signature? type type* 'TK' // key path getter
global ::= entity generic-signature? type type* 'Tk' // key path setter
global ::= type generic-signature 'TH' // key path equality
global ::= type generic-signature 'Th' // key path hasher
global ::= protocol 'TL' // protocol requirements base descriptor
global ::= assoc-type-name 'Tl' // associated type descriptor
global ::= assoc-type-name 'TM' // default associated type witness accessor (HISTORICAL)
global ::= type assoc-type-list protocol 'Tn' // associated conformance descriptor
global ::= type assoc-type-list protocol 'TN' // default associated conformance witness accessor
global ::= type protocol 'Tb' // base conformance descriptor
REABSTRACT-THUNK-TYPE ::= 'R' // reabstraction thunk
REABSTRACT-THUNK-TYPE ::= 'r' // reabstraction thunk (obsolete)
The `from-type` and `to-type` in a reabstraction thunk helper function
are always non-polymorphic ``<impl-function-type>`` types.
VALUE-WITNESS-KIND ::= 'al' // allocateBuffer
VALUE-WITNESS-KIND ::= 'ca' // assignWithCopy
VALUE-WITNESS-KIND ::= 'ta' // assignWithTake
VALUE-WITNESS-KIND ::= 'de' // deallocateBuffer
VALUE-WITNESS-KIND ::= 'xx' // destroy
VALUE-WITNESS-KIND ::= 'XX' // destroyBuffer
VALUE-WITNESS-KIND ::= 'Xx' // destroyArray
VALUE-WITNESS-KIND ::= 'CP' // initializeBufferWithCopyOfBuffer
VALUE-WITNESS-KIND ::= 'Cp' // initializeBufferWithCopy
VALUE-WITNESS-KIND ::= 'cp' // initializeWithCopy
VALUE-WITNESS-KIND ::= 'TK' // initializeBufferWithTakeOfBuffer
VALUE-WITNESS-KIND ::= 'Tk' // initializeBufferWithTake
VALUE-WITNESS-KIND ::= 'tk' // initializeWithTake
VALUE-WITNESS-KIND ::= 'pr' // projectBuffer
VALUE-WITNESS-KIND ::= 'xs' // storeExtraInhabitant
VALUE-WITNESS-KIND ::= 'xg' // getExtraInhabitantIndex
VALUE-WITNESS-KIND ::= 'Cc' // initializeArrayWithCopy
VALUE-WITNESS-KIND ::= 'Tt' // initializeArrayWithTakeFrontToBack
VALUE-WITNESS-KIND ::= 'tT' // initializeArrayWithTakeBackToFront
VALUE-WITNESS-KIND ::= 'ug' // getEnumTag
VALUE-WITNESS-KIND ::= 'up' // destructiveProjectEnumData
VALUE-WITNESS-KIND ::= 'ui' // destructiveInjectEnumTag
``<VALUE-WITNESS-KIND>`` differentiates the kinds of value
witness functions for a type.
global ::= generic-signature? type 'WOy' // Outlined copy
global ::= generic-signature? type 'WOe' // Outlined consume
global ::= generic-signature? type 'WOr' // Outlined retain
global ::= generic-signature? type 'WOs' // Outlined release
global ::= generic-signature? type 'WOb' // Outlined initializeWithTake
global ::= generic-signature? type 'WOc' // Outlined initializeWithCopy
global ::= generic-signature? type 'WOd' // Outlined assignWithTake
global ::= generic-signature? type 'WOf' // Outlined assignWithCopy
global ::= generic-signature? type 'WOh' // Outlined destroy
entity ::= nominal-type // named type declaration
entity ::= context entity-spec static? curry-thunk?
static ::= 'Z'
curry-thunk ::= 'Tc'
label-list ::= empty-list // represents complete absence of parameter labels
label-list ::= ('_' | identifier)* // '_' is inserted as placeholder for empty label,
// since the number of labels should match the number of parameters
// The leading type is the function type
entity-spec ::= label-list type file-discriminator? 'fC' // allocating constructor
entity-spec ::= label-list type file-discriminator? 'fc' // non-allocating constructor
entity-spec ::= type 'fU' INDEX // explicit anonymous closure expression
entity-spec ::= type 'fu' INDEX // implicit anonymous closure
entity-spec ::= 'fA' INDEX // default argument N+1 generator
entity-spec ::= 'fi' // non-local variable initializer
entity-spec ::= 'fP' // property wrapper backing initializer
entity-spec ::= 'fD' // deallocating destructor; untyped
entity-spec ::= 'fd' // non-deallocating destructor; untyped
entity-spec ::= 'fE' // ivar destroyer; untyped
entity-spec ::= 'fe' // ivar initializer; untyped
entity-spec ::= 'Tv' NATURAL // outlined global variable (from context function)
entity-spec ::= 'Te' bridge-spec // outlined objective c method call
entity-spec ::= decl-name label-list function-signature generic-signature? 'F' // function
entity-spec ::= label-list type file-discriminator? 'i' ACCESSOR // subscript
entity-spec ::= decl-name label-list? type 'v' ACCESSOR // variable
entity-spec ::= decl-name type 'fp' // generic type parameter
entity-spec ::= decl-name type 'fo' // enum element (currently not used)
entity-spec ::= identifier 'Qa' // associated type declaration
ACCESSOR ::= 'm' // materializeForSet
ACCESSOR ::= 's' // setter
ACCESSOR ::= 'g' // getter
ACCESSOR ::= 'G' // global getter
ACCESSOR ::= 'w' // willSet
ACCESSOR ::= 'W' // didSet
ACCESSOR ::= 'r' // read
ACCESSOR ::= 'M' // modify (temporary)
ACCESSOR ::= 'a' ADDRESSOR-KIND // mutable addressor
ACCESSOR ::= 'l' ADDRESSOR-KIND // non-mutable addressor
ACCESSOR ::= 'p' // pseudo accessor referring to the storage itself
ADDRESSOR-KIND ::= 'u' // unsafe addressor (no owner)
ADDRESSOR-KIND ::= 'O' // owning addressor (non-native owner), not used anymore
ADDRESSOR-KIND ::= 'o' // owning addressor (native owner), not used anymore
ADDRESSOR-KIND ::= 'p' // pinning addressor (native owner), not used anymore
decl-name ::= identifier
decl-name ::= identifier 'L' INDEX // locally-discriminated declaration
decl-name ::= identifier identifier 'LL' // file-discriminated declaration
decl-name ::= identifier 'L' RELATED-DISCRIMINATOR // related declaration
file-discriminator ::= identifier 'Ll' // anonymous file-discriminated declaration
The identifier in a ``<file-discriminator>`` and the second identifier in a
file-discriminated ``<decl-name>`` is a string that represents the file the
original declaration came from. It should be considered unique within the
enclosing module. The first identifier is the name of the entity. Not all
declarations marked ``private`` declarations will use this mangling; if the
entity's context is enough to uniquely identify the entity, the simple
``identifier`` form is preferred.
Twenty operators of the form 'LA', 'LB', etc. are reserved to described
entities related to the entity whose name is provided. For example, 'LE' and
'Le' in the "SC" module are used to represent the structs synthesized by the
Clang importer for various "error code" enums.
Outlined bridged Objective C method call mangling includes which parameters and
return value are bridged and the type of pattern outlined.
bridge-spec ::= bridged-kind bridged-param* bridged-return '_'
bridged-param ::= 'n' // not bridged parameter
bridged-param ::= 'b' // bridged parameter
bridged-return ::= 'n' // not bridged return
bridged-return ::= 'b' // bridged return
bridged-kind ::= 'm' // bridged method
bridged-kind ::= 'a' // bridged property (by address)
bridged-kind ::= 'p' // bridged property (by value)
Declaration Contexts
These manglings identify the enclosing context in which an entity was declared,
such as its enclosing module, function, or nominal type.
context ::= module
context ::= entity
context ::= entity module generic-signature? 'E'
An ``extension`` mangling is used whenever an entity's declaration context is
an extension *and* the entity being extended is in a different module. In this
case the extension's module is mangled first, followed by the entity being
extended. If the extension and the extended entity are in the same module, the
plain ``entity`` mangling is preferred. If the extension is constrained, the
constraints on the extension are mangled in its generic signature.
When mangling the context of a local entity within a constructor or
destructor, the non-allocating or non-deallocating variant is used.
module ::= identifier // module name
module ::= known-module // abbreviation
context ::= entity identifier type-list 'XZ' // unknown runtime context
The runtime produces manglings of unknown runtime contexts when a declaration
context has no preserved runtime information, or when a declaration is encoded
in runtime in a way that the current runtime does not understand. These
manglings are unstable and may change between runs of the process.
known-module ::= 's' // Swift
known-module ::= 'SC' // Clang-importer-synthesized
known-module ::= 'So' // C and Objective-C
The Objective-C module is used as the context for mangling Objective-C
classes as ``<type>``\ s.
any-generic-type ::= substitution
any-generic-type ::= context decl-name 'C' // nominal class type
any-generic-type ::= context decl-name 'O' // nominal enum type
any-generic-type ::= context decl-name 'V' // nominal struct type
any-generic-type ::= context decl-name 'XY' // unknown nominal type
any-generic-type ::= protocol 'P' // nominal protocol type
any-generic-type ::= standard-substitutions
standard-substitutions ::= 'S' KNOWN-TYPE-KIND // known nominal type substitution
standard-substitutions ::= 'S' NATURAL KNOWN-TYPE-KIND // repeated known type substitutions of the same kind
KNOWN-TYPE-KIND ::= 'A' // Swift.AutoreleasingUnsafeMutablePointer
KNOWN-TYPE-KIND ::= 'a' // Swift.Array
KNOWN-TYPE-KIND ::= 'B' // Swift.BinaryFloatingPoint
KNOWN-TYPE-KIND ::= 'b' // Swift.Bool
KNOWN-TYPE-KIND ::= 'c' // Swift.UnicodeScalar
KNOWN-TYPE-KIND ::= 'D' // Swift.Dictionary
KNOWN-TYPE-KIND ::= 'd' // Swift.Float64
KNOWN-TYPE-KIND ::= 'E' // Swift.Encodable
KNOWN-TYPE-KIND ::= 'e' // Swift.Decodable
KNOWN-TYPE-KIND ::= 'F' // Swift.FloatingPoint
KNOWN-TYPE-KIND ::= 'f' // Swift.Float32
KNOWN-TYPE-KIND ::= 'G' // Swift.RandomNumberGenerator
KNOWN-TYPE-KIND ::= 'H' // Swift.Hashable
KNOWN-TYPE-KIND ::= 'h' // Swift.Set
KNOWN-TYPE-KIND ::= 'I' // Swift.DefaultIndices
KNOWN-TYPE-KIND ::= 'i' // Swift.Int
KNOWN-TYPE-KIND ::= 'J' // Swift.Character
KNOWN-TYPE-KIND ::= 'j' // Swift.Numeric
KNOWN-TYPE-KIND ::= 'K' // Swift.BidirectionalCollection
KNOWN-TYPE-KIND ::= 'k' // Swift.RandomAccessCollection
KNOWN-TYPE-KIND ::= 'L' // Swift.Comparable
KNOWN-TYPE-KIND ::= 'l' // Swift.Collection
KNOWN-TYPE-KIND ::= 'M' // Swift.MutableCollection
KNOWN-TYPE-KIND ::= 'm' // Swift.RangeReplaceableCollection
KNOWN-TYPE-KIND ::= 'N' // Swift.ClosedRange
KNOWN-TYPE-KIND ::= 'n' // Swift.Range
KNOWN-TYPE-KIND ::= 'O' // Swift.ObjectIdentifier
KNOWN-TYPE-KIND ::= 'P' // Swift.UnsafePointer
KNOWN-TYPE-KIND ::= 'p' // Swift.UnsafeMutablePointer
KNOWN-TYPE-KIND ::= 'Q' // Swift.Equatable
KNOWN-TYPE-KIND ::= 'q' // Swift.Optional
KNOWN-TYPE-KIND ::= 'R' // Swift.UnsafeBufferPointer
KNOWN-TYPE-KIND ::= 'r' // Swift.UnsafeMutableBufferPointer
KNOWN-TYPE-KIND ::= 'S' // Swift.String
KNOWN-TYPE-KIND ::= 's' // Swift.Substring
KNOWN-TYPE-KIND ::= 'T' // Swift.Sequence
KNOWN-TYPE-KIND ::= 't' // Swift.IteratorProtocol
KNOWN-TYPE-KIND ::= 'U' // Swift.UnsignedInteger
KNOWN-TYPE-KIND ::= 'u' // Swift.UInt
KNOWN-TYPE-KIND ::= 'V' // Swift.UnsafeRawPointer
KNOWN-TYPE-KIND ::= 'v' // Swift.UnsafeMutableRawPointer
KNOWN-TYPE-KIND ::= 'W' // Swift.UnsafeRawBufferPointer
KNOWN-TYPE-KIND ::= 'w' // Swift.UnsafeMutableRawBufferPointer
KNOWN-TYPE-KIND ::= 'X' // Swift.RangeExpression
KNOWN-TYPE-KIND ::= 'x' // Swift.Strideable
KNOWN-TYPE-KIND ::= 'Y' // Swift.RawRepresentable
KNOWN-TYPE-KIND ::= 'y' // Swift.StringProtocol
KNOWN-TYPE-KIND ::= 'Z' // Swift.SignedInteger
KNOWN-TYPE-KIND ::= 'z' // Swift.BinaryInteger
protocol ::= context decl-name
protocol ::= standard-substitutions
type ::= 'Bb' // Builtin.BridgeObject
type ::= 'BB' // Builtin.UnsafeValueBuffer
type ::= 'Bc' // Builtin.RawUnsafeContinuation
type ::= 'BD' // Builtin.DefaultActorStorage
type ::= 'Bf' NATURAL '_' // Builtin.Float<n>
type ::= 'Bi' NATURAL '_' // Builtin.Int<n>
type ::= 'BI' // Builtin.IntLiteral
type ::= 'Bj' // Builtin.Job
type ::= 'BO' // Builtin.UnknownObject (no longer a distinct type, but still used for AnyObject)
type ::= 'Bo' // Builtin.NativeObject
type ::= 'Bp' // Builtin.RawPointer
type ::= 'Bt' // Builtin.SILToken
type ::= type 'Bv' NATURAL '_' // Builtin.Vec<n>x<type>
type ::= 'Bw' // Builtin.Word
type ::= function-signature 'c' // function type (escaping)
type ::= function-signature 'X' FUNCTION-KIND // special function type
type ::= bound-generic-type
type ::= type 'Sg' // optional type, shortcut for: type 'ySqG'
type ::= type 'Xo' // @unowned type
type ::= type 'Xu' // @unowned(unsafe) type
type ::= type 'Xw' // @weak type
type ::= impl-function-type 'XF' // function implementation type (currently unused)
type ::= type 'Xb' // SIL @box type (deprecated)
type ::= type-list 'Xx' // SIL box type
type ::= type-list type-list generic-signature 'XX'
// Generic SIL box type
type ::= type 'XD' // dynamic self type
type ::= type 'm' // metatype without representation
type ::= type 'XM' METATYPE-REPR // metatype with representation
type ::= type 'Xp' // existential metatype without representation
type ::= type 'Xm' METATYPE-REPR // existential metatype with representation
type ::= 'Xe' // error or unresolved type
bound-generic-type ::= type 'y' (type* '_')* type* retroactive-conformance* 'G' // one type-list per nesting level of type
bound-generic-type ::= substitution
FUNCTION-KIND ::= 'f' // @thin function type
FUNCTION-KIND ::= 'U' // uncurried function type (currently not used)
FUNCTION-KIND ::= 'K' // @auto_closure function type (noescape)
FUNCTION-KIND ::= 'B' // objc block function type
FUNCTION-KIND ::= 'zB' C-TYPE // objc block type with non-canonical C type
FUNCTION-KIND ::= 'L' // objc block function type with canonical C type (escaping) (DWARF only; otherwise use 'B' or 'zB' C-TYPE)
FUNCTION-KIND ::= 'C' // C function pointer type
FUNCTION-KIND ::= 'zC' C-TYPE // C function pointer type with with non-canonical C type
FUNCTION-KIND ::= 'A' // @auto_closure function type (escaping)
FUNCTION-KIND ::= 'E' // function type (noescape)
FUNCTION-KIND ::= 'F' // @differentiable function type
FUNCTION-KIND ::= 'G' // @differentiable function type (escaping)
FUNCTION-KIND ::= 'H' // @differentiable(linear) function type
FUNCTION-KIND ::= 'I' // @differentiable(linear) function type (escaping)
C-TYPE is mangled according to the Itanium ABI, and prefixed with the length.
Non-ASCII identifiers are preserved as-is; we do not use Punycode.
function-signature ::= params-type params-type async? throws? // results and parameters
params-type ::= type 'z'? 'h'? // tuple in case of multiple parameters or a single parameter with a single tuple type
// with optional inout convention, shared convention. parameters don't have labels,
// they are mangled separately as part of the entity.
params-type ::= empty-list // shortcut for no parameters
async ::= 'Y' // 'async' annotation on function types
throws ::= 'K' // 'throws' annotation on function types
type-list ::= list-type '_' list-type* // list of types
type-list ::= empty-list
// FIXME: Consider replacing 'h' with a two-char code
list-type ::= type identifier? 'z'? 'h'? 'n'? 'd'? // type with optional label, inout convention, shared convention, owned convention, and variadic specifier
METATYPE-REPR ::= 't' // Thin metatype representation
METATYPE-REPR ::= 'T' // Thick metatype representation
METATYPE-REPR ::= 'o' // ObjC metatype representation
type ::= archetype
type ::= associated-type
type ::= any-generic-type
type ::= protocol-list 'p' // existential type
type ::= protocol-list superclass 'Xc' // existential type with superclass
type ::= protocol-list 'Xl' // existential type with AnyObject
type ::= type-list 't' // tuple
type ::= type generic-signature 'u' // generic type
type ::= 'x' // generic param, depth=0, idx=0
type ::= 'q' GENERIC-PARAM-INDEX // dependent generic parameter
type ::= type assoc-type-name 'qa' // associated type of non-generic param
type ::= assoc-type-name 'Qy' GENERIC-PARAM-INDEX // associated type
type ::= assoc-type-name 'Qz' // shortcut for 'Qyz'
type ::= assoc-type-list 'QY' GENERIC-PARAM-INDEX // associated type at depth
type ::= assoc-type-list 'QZ' // shortcut for 'QYz'
type ::= type assoc-type-name 'Qx' // associated type relative to base `type`
type ::= type assoc-type-list 'QX' // associated type relative to base `type`
protocol-list ::= protocol '_' protocol*
protocol-list ::= empty-list
assoc-type-list ::= assoc-type-name '_' assoc-type-name*
archetype ::= associated-type
associated-type ::= substitution
associated-type ::= protocol 'QP' // self type of protocol
associated-type ::= archetype identifier 'Qa' // associated type
assoc-type-name ::= identifier // associated type name without protocol
assoc-type-name ::= identifier protocol 'P' //
empty-list ::= 'y'
Associated types use an abbreviated mangling when the base generic parameter
or associated type is constrained by a single protocol requirement. The
associated type in this case can be referenced unambiguously by name alone.
If the base has multiple conformance constraints, then the protocol name is
mangled in to disambiguate.
impl-function-type ::= type* 'I' FUNC-ATTRIBUTES '_'
impl-function-type ::= type* generic-signature 'I' FUNC-ATTRIBUTES '_'
PATTERN-SUBS ::= 's' // has pattern substitutions
INVOCATION-SUB ::= 'I' // has invocation substitutions
CALLEE-ESCAPE ::= 'e' // @escaping (inverse of SIL @noescape)
DIFFERENTIABLE ::= 'd' // @differentiable
LINEAR ::= 'l' // @differentiable(linear)
CALLEE-CONVENTION ::= 'y' // @callee_unowned
CALLEE-CONVENTION ::= 'g' // @callee_guaranteed
CALLEE-CONVENTION ::= 'x' // @callee_owned
CALLEE-CONVENTION ::= 't' // thin
FUNC-REPRESENTATION ::= 'B' // C block invocation function
FUNC-REPRESENTATION ::= 'zB' C-TYPE // C block invocation function with non-canonical C type
FUNC-REPRESENTATION ::= 'C' // C global function
FUNC-REPRESENTATION ::= 'zC' C-TYPE // C global function with non-canonical C type
FUNC-REPRESENTATION ::= 'M' // Swift method
FUNC-REPRESENTATION ::= 'J' // ObjC method
FUNC-REPRESENTATION ::= 'K' // closure
FUNC-REPRESENTATION ::= 'W' // protocol witness
COROUTINE-KIND ::= 'A' // yield-once coroutine
COROUTINE-KIND ::= 'G' // yield-many coroutine
ASYNC ::= 'H' // @async
PARAM-CONVENTION ::= 'i' // indirect in
PARAM-CONVENTION ::= 'c' // indirect in constant
PARAM-CONVENTION ::= 'l' // indirect inout
PARAM-CONVENTION ::= 'b' // indirect inout aliasable
PARAM-CONVENTION ::= 'n' // indirect in guaranteed
PARAM-CONVENTION ::= 'x' // direct owned
PARAM-CONVENTION ::= 'y' // direct unowned
PARAM-CONVENTION ::= 'g' // direct guaranteed
PARAM-CONVENTION ::= 'e' // direct deallocating
PARAM-DIFFERENTIABILITY ::= 'w' // @noDerivative
RESULT-CONVENTION ::= 'r' // indirect
RESULT-CONVENTION ::= 'o' // owned
RESULT-CONVENTION ::= 'd' // unowned
RESULT-CONVENTION ::= 'u' // unowned inner pointer
RESULT-CONVENTION ::= 'a' // auto-released
RESULT-DIFFERENTIABILITY ::= 'w' // @noDerivative
For the most part, manglings follow the structure of formal language
types. However, in some cases it is more useful to encode the exact
implementation details of a function type.
#if SWIFT_VERSION >= 5.1
type ::= 'Qr' // opaque result type (of current decl)
type ::= opaque-type-decl-name bound-generic-args 'Qo' INDEX // opaque type
opaque-type-decl-name ::= entity 'QO' // opaque result type of specified decl
#if SWIFT_VERSION >= 5.4
type ::= 'Qu' // opaque result type (of current decl)
// used for ObjC class runtime name purposes.
Opaque return types have a special short representation in the mangling of
their defining entity. In structural position, opaque types are fully qualified
by mangling the defining entity for the opaque declaration and the substitutions
into the defining entity's generic environment.
The ``type*`` list contains parameter and return types (including the error
result), in that order.
The number of parameters and results must match with the number of
``<PARAM-CONVENTION>`` and ``<RESULT-CONVENTION>`` characters after the
The ``<generic-signature>`` is used if the function is polymorphic.
DWARF debug info and USRs also mangle sugared types, adding the following
any-generic-type ::= context decl-name 'a' // typealias type
type ::= base-type "XSq" // sugared Optional type
type ::= base-type "XSa" // sugared Array type
type ::= key-type value-type "XSD" // sugared Dictionary type
type ::= base-type "XSp" // sugared Paren type
protocol-conformance-context ::= protocol module generic-signature?
protocol-conformance ::= type protocol-conformance-context
``<protocol-conformance>`` refers to a type's conformance to a protocol. The
named module is the one containing the extension or type declaration that
declared the conformance.
protocol-conformance ::= type protocol
If ``type`` is a generic parameter or associated type of one, then no module
is mangled, because the conformance must be resolved from the generic
protocol-conformance ::= context identifier protocol identifier generic-signature? // Property behavior conformance
Property behaviors are implemented using private protocol conformances.
concrete-protocol-conformance ::= type protocol-conformance-ref any-protocol-conformance-list 'HC'
protocol-conformance-ref ::= protocol 'HP' // same module as conforming type
protocol-conformance-ref ::= protocol 'Hp' // same module as protocol
protocol-conformance-ref ::= protocol module // "retroactive"
any-protocol-conformance ::= concrete-protocol-conformance
any-protocol-conformance ::= dependent-protocol-conformance
any-protocol-conformance-list ::= any-protocol-conformance '_' any-protocol-conformance-list
any-protocol-conformance-list ::= empty-list
dependent-protocol-conformance ::= type protocol 'HD' DEPENDENT-CONFORMANCE-INDEX
dependent-protocol-conformance ::= dependent-protocol-conformance protocol 'HI' DEPENDENT-CONFORMANCE-INDEX
dependent-protocol-conformance ::= dependent-protocol-conformance
dependent-associated-conformance 'HA' DEPENDENT-CONFORMANCE-INDEX
dependent-associated-conformance ::= type protocol
dependent-protocol-conformance ::= dependent-protocol-conformance opaque-type 'HO'
A compact representation used to represent mangled protocol conformance witness
arguments at runtime. The ``module`` is only specified for conformances that
are "retroactive", meaning that the context in which the conformance is defined
is in neither the protocol or type module. For a non-retroactive conformance
where both the type *and* the protocol are in the same module, or for
synthesized conformances that have no owning module, the "HP" operator is
preferred. The concrete protocol conformances that follow are for the
conditional conformance requirements.
Dependent protocol conformances mangle the access path required to extract a
protocol conformance from some conformance passed into the environment. The
first case (operator "HD") is the leaf requirement, containing a dependent type
and the protocol it conforms to. The remaining dependent protocol conformance
manglings describe lookups performed on their child dependent protocol
conformances. The "HI" operator retrieves the named inherited protocol from the
witness table produced by the child. The "HA" operator refers to an associated
conformance within the witness table, identified by the dependent type and
protocol. In all cases, the DEPENDENT-CONFORMANCE-INDEX is an INDEX value
indicating the position of the appropriate value within the generic environment
(for "HD") or witness table (for "HI" and "HA") when it is known to be at a
fixed position. An index of 1 ("0\_") is used to indicate "unknown"; all other
values are adjusted by 2. That these indexes are not 0-based is a bug that's
now codified into the ABI; the index 0 is therefore reserved.
generic-signature ::= requirement* 'l' // one generic parameter
generic-signature ::= requirement* 'r' GENERIC-PARAM-COUNT* 'l'
GENERIC-PARAM-COUNT ::= 'z' // zero parameters
GENERIC-PARAM-COUNT ::= INDEX // N+1 parameters
requirement ::= protocol 'R' GENERIC-PARAM-INDEX // protocol requirement
requirement ::= protocol assoc-type-name 'Rp' GENERIC-PARAM-INDEX // protocol requirement on associated type
requirement ::= protocol assoc-type-list 'RP' GENERIC-PARAM-INDEX // protocol requirement on associated type at depth
requirement ::= protocol substitution 'RQ' // protocol requirement with substitution
requirement ::= type 'Rb' GENERIC-PARAM-INDEX // base class requirement
requirement ::= type assoc-type-name 'Rc' GENERIC-PARAM-INDEX // base class requirement on associated type
requirement ::= type assoc-type-list 'RC' GENERIC-PARAM-INDEX // base class requirement on associated type at depth
requirement ::= type substitution 'RB' // base class requirement with substitution
requirement ::= type 'Rs' GENERIC-PARAM-INDEX // same-type requirement
requirement ::= type assoc-type-name 'Rt' GENERIC-PARAM-INDEX // same-type requirement on associated type
requirement ::= type assoc-type-list 'RT' GENERIC-PARAM-INDEX // same-type requirement on associated type at depth
requirement ::= type substitution 'RS' // same-type requirement with substitution
requirement ::= type 'Rl' GENERIC-PARAM-INDEX LAYOUT-CONSTRAINT // layout requirement
requirement ::= type assoc-type-name 'Rm' GENERIC-PARAM-INDEX LAYOUT-CONSTRAINT // layout requirement on associated type
requirement ::= type assoc-type-list 'RM' GENERIC-PARAM-INDEX LAYOUT-CONSTRAINT // layout requirement on associated type at depth
requirement ::= type substitution 'RM' LAYOUT-CONSTRAINT // layout requirement with substitution
GENERIC-PARAM-INDEX ::= 'z' // depth = 0, idx = 0
GENERIC-PARAM-INDEX ::= INDEX // depth = 0, idx = N+1
GENERIC-PARAM-INDEX ::= 'd' INDEX INDEX // depth = M+1, idx = N
LAYOUT-CONSTRAINT ::= 'N' // NativeRefCountedObject
LAYOUT-CONSTRAINT ::= 'R' // RefCountedObject
LAYOUT-CONSTRAINT ::= 'T' // Trivial
LAYOUT-CONSTRAINT ::= 'D' // NativeClass
LAYOUT-CONSTRAINT ::= 'e' LAYOUT-SIZE // Trivial of exact size
LAYOUT-CONSTRAINT ::= 'M' LAYOUT-SIZE-AND-ALIGNMENT // Trivial of size at most N bits
LAYOUT-CONSTRAINT ::= 'm' LAYOUT-SIZE // Trivial of size at most N bits
LAYOUT-CONSTRAINT ::= 'U' // Unknown layout
LAYOUT-SIZE ::= INDEX // Size only
LAYOUT-SIZE-AND-ALIGNMENT ::= INDEX INDEX // Size followed by alignment
A generic signature begins with an optional list of requirements.
The ``<GENERIC-PARAM-COUNT>`` describes the number of generic parameters at
each depth of the signature. As a special case, no ``<GENERIC-PARAM-COUNT>``
values indicates a single generic parameter at the outermost depth::
x_xCru // <T_0_0> T_0_0 -> T_0_0
d_0__xCr_0_u // <T_0_0><T_1_0, T_1_1> T_0_0 -> T_1_1
A generic signature must only precede an operator character which is different
from any character in a ``<GENERIC-PARAM-COUNT>``.
retroactive-conformance ::= any-protocol-conformance 'g' INDEX
When a protocol conformance used to satisfy one of a bound generic type's
generic requirements is retroactive (i.e., it is specified in a module other
than the module of the conforming type or the conformed-to protocol), it is
mangled with its offset into the set of conformance requirements, the
root protocol conformance, and the suffix 'g'.
identifier ::= substitution
identifier ::= NATURAL IDENTIFIER-STRING // identifier without word substitutions
identifier ::= '0' IDENTIFIER-PART // identifier with word substitutions
IDENTIFIER-PART ::= [a-z] // word substitution (except the last one)
IDENTIFIER-PART ::= [A-Z] // last word substitution in identifier
IDENTIFIER-CHAR ::= [_$a-zA-Z0-9]
``<identifier>`` is run-length encoded: the natural indicates how many
characters follow. Operator characters are mapped to letter characters as
given. In neither case can an identifier start with a digit, so
there's no ambiguity with the run-length.
If the run-length start with a ``0`` the identifier string contains
word substitutions. A word is a sub-string of an identifier which contains
letters and digits ``[A-Za-z0-9]``. Words are separated by underscores
``_``. In addition a new word begins with an uppercase letter ``[A-Z]``
if the previous character is not an uppercase letter::
Abc1DefG2HI // contains four words 'Abc1', 'Def' and 'G2' and 'HI'
_abc1_def_G2hi // contains three words 'abc1', 'def' and G2hi
The words of all identifiers, which are encoded in the current mangling are
enumerated and assigned to a letter: a = first word, b = second word, etc.
An identifier containing word substitutions is a sequence of run-length encoded
sub-strings and references to previously mangled words.
All but the last word-references are lowercase letters and the last one is an
uppercase letter. If there is no literal sub-string after the last
word-reference, the last word-reference is followed by a ``0``.
Let's assume the current mangling already encoded the identifier ``AbcDefGHI``::
02Myac1_B // expands to: MyAbcGHI_Def
A maximum of 26 words in a mangling can be used for substitutions.
identifier ::= '00' natural '_'? IDENTIFIER-CHAR+ // '_' is inserted if the identifier starts with a digit or '_'.
Identifiers that contain non-ASCII characters are encoded using the Punycode
algorithm specified in RFC 3492, with the modifications that ``_`` is used
as the encoding delimiter, and uppercase letters A through J are used in place
of digits 0 through 9 in the encoding character set. The mangling then
consists of an ``00`` followed by the run length of the encoded string and the
encoded string itself. For example, the identifier ``vergüenza`` is mangled
to ``0012vergenza_JFa``. (The encoding in standard Punycode would be
If the encoded string starts with a digit or an ``_``, an additional ``_`` is
inserted between the run length and the encoded string.
identifier ::= identifier 'o' OPERATOR-FIXITY
OPERATOR-FIXITY ::= 'p' // prefix operator
OPERATOR-FIXITY ::= 'P' // postfix operator
OPERATOR-FIXITY ::= 'i' // infix operator
OPERATOR-CHAR ::= 'a' // & 'and'
OPERATOR-CHAR ::= 'c' // @ 'commercial at'
OPERATOR-CHAR ::= 'd' // / 'divide'
OPERATOR-CHAR ::= 'e' // = 'equals'
OPERATOR-CHAR ::= 'g' // > 'greater'
OPERATOR-CHAR ::= 'l' // < 'less'
OPERATOR-CHAR ::= 'm' // * 'multiply'
OPERATOR-CHAR ::= 'n' // ! 'not'
OPERATOR-CHAR ::= 'o' // | 'or'
OPERATOR-CHAR ::= 'p' // + 'plus'
OPERATOR-CHAR ::= 'q' // ? 'question'
OPERATOR-CHAR ::= 'r' // % 'remainder'
OPERATOR-CHAR ::= 's' // - 'subtract'
OPERATOR-CHAR ::= 't' // ~ 'tilde'
OPERATOR-CHAR ::= 'x' // ^ 'xor'
OPERATOR-CHAR ::= 'z' // . 'zperiod'
If an identifier is followed by an ``o`` its text is interpreted as an
operator. Each lowercase character maps to an operator character
Operators that contain non-ASCII characters are mangled by first mapping the
ASCII operator characters to letters as for pure ASCII operator names, then
Punycode-encoding the substituted string.
For example, the infix operator ``«+»`` is mangled to
``007p_qcaDcoi`` (``p_qcaDc`` being the encoding of the substituted
string ``«p»``).
substitution ::= 'A' INDEX // substitution of N+26
substitution ::= 'A' SUBST_IDX* LAST-SUBST-IDX // One or more consecutive substitutions of N < 26
SUBST-IDX ::= [a-z]
``<substitution>`` is a back-reference to a previously mangled entity. The mangling
algorithm maintains a mapping of entities to substitution indices as it runs.
When an entity that can be represented by a substitution (a module, nominal
type, or protocol) is mangled, a substitution is first looked for in the
substitution map, and if it is present, the entity is mangled using the
associated substitution index. Otherwise, the entity is mangled normally, and
it is then added to the substitution map and associated with the next
available substitution index.
For example, in mangling a function type
``(zim.zang.zung, zim.zang.zung, zim.zippity) -> zim.zang.zoo`` (with module
``zim`` and class ``zim.zang``),
the recurring contexts ``zim``, ``zim.zang``, and ``zim.zang.zung``
will be mangled using substitutions after being mangled
for the first time. The first argument type will mangle in long form,
``3zim4zang4zung``, and in doing so, ``zim`` will acquire substitution ``AA``,
``zim.zang`` will acquire substitution ``AB``, and ``zim.zang.zung`` will
acquire ``AC``. The second argument is the same as the first and will mangle
using its substitution, ``AC``. The
third argument type will mangle using the substitution for ``zim``,
``AA7zippity``. (It also acquires substitution ``AD`` which would be used
if it mangled again.) The result type will mangle using the substitution for
``zim.zang``, ``AB3zoo`` (and acquire substitution ``AE``).
There are some pre-defined substitutions, see ``KNOWN-TYPE-KIND``.
If the mangling contains two or more consecutive substitutions, it can be
abbreviated with the ``A`` substitution. Similar to word-substitutions the
index is encoded as letters, whereas the last letter is uppercase::
AaeB // equivalent to A_A4_A0_
Repeated substitutions are encoded with a natural prefix number::
A3a2B // equivalent to AaaabB
Numbers and Indexes
INDEX ::= '_' // 0
INDEX ::= NATURAL '_' // N+1
NATURAL ::= [1-9] [0-9]*
NATURAL_ZERO ::= [0-9]+
``<INDEX>`` is a production for encoding numbers in contexts that can't
end in a digit; it's optimized for encoding smaller numbers.
Function Specializations
specialization ::= type '_' type* 'Tg' SPEC-INFO // Generic re-abstracted specialization
specialization ::= type '_' type* 'TB' SPEC-INFO // Alternative mangling for generic re-abstracted specializations,
// used for functions with re-abstracted resilient parameter types.
specialization ::= type '_' type* 'Ts' SPEC-INFO // Generic re-abstracted prespecialization
specialization ::= type '_' type* 'TG' SPEC-INFO // Generic not re-abstracted specialization
specialization ::= type '_' type* 'Ti' SPEC-INFO // Inlined function with generic substitutions.
The types are the replacement types of the substitution list.
specialization ::= type 'Tp' SPEC-INFO // Partial generic specialization
specialization ::= type 'TP' SPEC-INFO // Partial generic specialization, not re-abstracted
The type is the function type of the specialized function.
specialization ::= spec-arg* 'Tf' SPEC-INFO ARG-SPEC-KIND* '_' ARG-SPEC-KIND // Function signature specialization kind
The ``<ARG-SPEC-KIND>`` describes how arguments are specialized.
Some kinds need arguments, which precede ``Tf``.
spec-arg ::= identifier
spec-arg ::= type
PASSID ::= '0' // AllocBoxToStack,
PASSID ::= '1' // ClosureSpecializer,
PASSID ::= '2' // CapturePromotion,
PASSID ::= '3' // CapturePropagation,
PASSID ::= '4' // FunctionSignatureOpts,
PASSID ::= '5' // GenericSpecializer,
FRAGILE ::= 'q'
ARG-SPEC-KIND ::= 'n' // Unmodified argument
ARG-SPEC-KIND ::= 'c' // Consumes n 'type' arguments which are closed over types in argument order
// and one 'identifier' argument which is the closure symbol name
ARG-SPEC-KIND ::= 'p' CONST-PROP // Constant propagated argument
ARG-SPEC-KIND ::= 'e' 'D'? 'G'? 'X'? // Generic argument, with optional dead, owned=>guaranteed or exploded-specifier
ARG-SPEC-KIND ::= 'd' 'G'? 'X'? // Dead argument, with optional owned=>guaranteed or exploded-specifier
ARG-SPEC-KIND ::= 'g' 'X'? // Owned => Guaranteed,, with optional exploded-specifier
ARG-SPEC-KIND ::= 'x' // Exploded
ARG-SPEC-KIND ::= 'i' // Box to value
ARG-SPEC-KIND ::= 's' // Box to stack
CONST-PROP ::= 'f' // Consumes one identifier argument which is a function symbol name
CONST-PROP ::= 'g' // Consumes one identifier argument which is a global symbol name
CONST-PROP ::= 'i' NATURAL_ZERO // 64-bit-integer
CONST-PROP ::= 'd' NATURAL_ZERO // float-as-64-bit-integer
CONST-PROP ::= 's' ENCODING // string literal. Consumes one identifier argument.
ENCODING ::= 'b' // utf8
ENCODING ::= 'w' // utf16
ENCODING ::= 'c' // utf16
If the first character of the string literal is a digit ``[0-9]`` or an
underscore ``_``, the identifier for the string literal is prefixed with an
additional underscore ``_``.
Conventions for foreign symbols
Swift interoperates with multiple other languages - C, C++, Objective-C, and
Objective-C++. Each of these languages defines their own mangling conventions,
so Swift must take care to follow them. However, these conventions do not cover
Swift-specific symbols like Swift type metadata for foreign types, so Swift uses
its own mangling scheme for those symbols.
Importing C and C++ structs
Types imported from C and C++ are imported as if they are located in the ``__C``
module, regardless of the actual Clang module that they are coming from. This
can be observed when mangling a Swift function that accepts a C/C++ struct as a
C++ module ``CxxStructModule``:
.. code-block:: c++
struct CxxStruct {};
inline void cxxFunction(CxxStruct s) {}
Swift module ``main`` that imports ``CxxStructModule``:
.. code-block:: swift
import CxxStructModule
public func swiftFunction(_ s: CxxStruct) {}
Resulting symbols (showing only Itanium-mangled C++ symbols for brevity):
.. code::
_Z11cxxFunction9CxxStruct // -> cxxFunction(CxxStruct)
s4main13swiftFunctionyySo9CxxStructVF // -> main.swiftFunction(__C.CxxStruct) -> ()
The reason for ignoring the Clang module and always putting C and C++ types into
``__C`` at the Swift ABI level is that the Clang module is not a part of the C
or C++ ABI. When owners of C and C++ Clang modules decide what changes are
ABI-compatible or not, they will likely take into account C and C++ ABI, but not
the Swift ABI. Therefore, Swift ABI can only encode information about a C or C++
type that the C and C++ ABI already encodes in order to remain compatible with
future versions of libraries that evolve according to C and C++ ABI
compatibility principles.
The C/C++ compiler does not generate Swift metadata symbols and value witness
tables for C and C++ types. To make a foreign type usable in Swift in the same
way as a native type, the Swift compiler must generate these symbols.
Specifically, each Swift module that uses a given C or C++ type generates the
necessary Swift symbols. For the example above the Swift compiler will generate following
nominal type descriptor symbol for ``CxxStruct`` while compiling the ``main`` module:
.. code::
sSo9CxxStructVMn // -> nominal type descriptor for __C.CxxStruct
Importing C++ class template instantiations
A class template instantiation is imported as a struct named
``__CxxTemplateInst`` plus Itanium mangled type of the instantiation (see the
``type`` production in the Itanium specification). Note that Itanium mangling is
used on all platforms, regardless of the ABI of the C++ toolchain, to ensure
that the mangled name is a valid Swift type name (this is not the case for MSVC
mangled names). A prefix with a double underscore (to ensure we have a reserved
C++ identifier) is added to limit the possibility for conflicts with names of
user-defined structs. The struct is notionally defined in the ``__C`` module,
similarly to regular C and C++ structs and classes. Consider the following C++
.. code-block:: c++
template<class T>
struct MagicWrapper {
T t;
struct MagicNumber {};
typedef MagicWrapper<MagicNumber> WrappedMagicNumber;
``WrappedMagicNumber`` is imported as a typealias for struct
``__CxxTemplateInst12MagicWrapperI11MagicNumberE``. Interface of the imported
module looks as follows:
.. code-block:: swift
struct __CxxTemplateInst12MagicWrapperI11MagicNumberE {
var t: MagicNumber
struct MagicNumber {}
typealias WrappedMagicNumber = __CxxTemplateInst12MagicWrapperI11MagicNumberE