include/swift/AST/ReferenceCounting.h

//===--- ReferenceCounting.h ------------------------------------*- 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
//
//===----------------------------------------------------------------------===//

#ifndef SWIFT_AST_REFERENCE_COUNTING_H
#define SWIFT_AST_REFERENCE_COUNTING_H

namespace swift {

/// The kind of reference counting implementation a heap object uses.
enum class ReferenceCounting : uint8_t {
  /// The object uses native Swift reference counting.
  Native,

  /// The object uses ObjC reference counting.
  ///
  /// When ObjC interop is enabled, native Swift class objects are also ObjC
  /// reference counting compatible. Swift non-class heap objects are never
  /// ObjC reference counting compatible.
  ///
  /// Blocks are always ObjC reference counting compatible.
  ObjC,

  /// The object uses _Block_copy/_Block_release reference counting.
  ///
  /// This is a strict subset of ObjC; all blocks are also ObjC reference
  /// counting compatible. The block is assumed to have already been moved to
  /// the heap so that _Block_copy returns the same object back.
  Block,

  /// The object has an unknown reference counting implementation.
  ///
  /// This uses maximally-compatible reference counting entry points in the
  /// runtime.
  Unknown,

  /// Cases prior to this one are binary-compatible with Unknown reference
  /// counting.
  LastUnknownCompatible = Unknown,

  /// The object has an unknown reference counting implementation and
  /// the reference value may contain extra bits that need to be masked.
  ///
  /// This uses maximally-compatible reference counting entry points in the
  /// runtime, with a masking layer on top. A bit inside the pointer is used
  /// to signal native Swift refcounting.
  Bridge,

  /// The object uses ErrorType's reference counting entry points.
  Error,
};

} // end namespace swift

#endif