** ‼️ The official C++ interoperability documentation and status page is live at Swift.org and provides an up-to-date guide for mixing Swift and C++ ‼️ **

C++ Interoperability Status

Swift has some experimental ability to interoperate with C++. This document provides an overview of the status of the Swift and C++ interoperability support.

C++ to Swift Interoperability Status

Swift has the experimental ability to import a large subset of C++. This section of the document describes which C++ language and standard library features can be imported and used from Swift in an experimental manner.

Example

The following example demonstrates several interop features. It compiles and runs on main.

// cxx-types.h (mapped to CxxTypes module in module.modulemap)
#include <algorithm>
#include <vector>

using V = std::vector<long>;

// main.swift
import CxxTypes
import CxxStdlib

// We can extend C++ types in Swift.
extension V : RandomAccessCollection {
  public var startIndex: Int { 0 }
  public var endIndex: Int { size() }
}

// Create a vector with some data.
var numbers = V(4)
std.fill(numbers.beginMutating(), numbers.endMutating(), 41)

// Transform it using C++.
std.transform(numbers.beginMutating(), numbers.endMutating(),
              numbers.beginMutating()) { (element: Int) in
  return element + 1
}

// Loop over it in Swift.
for (index, element) in numbers.enumerated() {
  print("v[\(index)] = \(element)")
}

// We can also use anything in RandomAccessCollection, such as map and zip.
let strings = numbers.map { "\($0)" }
for (s, n) in zip(strings, numbers) {
  print("\(s) = \(n)")
}

Importing C++

There are currently two experimental ways to import C++ into Swift:

• Clang modules: can be imported into Swift. This requires a module map.
• Bridging header: can be imported into Swift. Headers included in the bridging header will be imported. Please note that support for importing C++ 20 modules isn’t implemented.

Both CMake and the Swift package manager can be configured to invoke Swift with the correct arguments to import C++ headers.

Note: C++ code is imported using the Objective-C++ language mode on Apple platforms.

Experimental C++ Language Support

This status table describes which of the following C++ language features can be used in Swift:

The following C++ code patterns or language features have specific mappings to Swift language features when imported in Swift:

Unless stated otherwise (i.e., imported reference types) all Swift features work with imported types. For example: use in generic contexts, protocol conformance, extensions, etc.

C++ Standard Library Support

Parts of libc++ can be imported and used from Swift. C++ standard library types are bridged directly to Swift, and there is not automatic bridging to native Swift types. This means that if an imported C++ API returns std::string, you will get a std::string value in Swift as well, and not Swift's String.

This status table describes which of the following C++ standard library features have some experimental support for using them in Swift. Please note that this is not a comprehensive list and other libc++ APIs that use the above supported C++ language features could be imported into Swift.

Known Issues

Inline Namespaces

• #58217: Swift's typechecker currently doesn't allow calling a function from an inline namespace when it's referenced through the parent namespace. Example of a test that fails: https://github.com/swiftlang/swift/blob/main/test/Interop/Cxx/namespace/inline-namespace-function-call-broken.swift

Swift to C++ Interoperability Status

This section of the document describes which Swift language and standard library features can be imported and used from C++.

Importing Swift

Swift has some experimental support for generating a header that can be imported by C++.

Swift Language Support

This status table describes which of the following Swift language features have some experimental support for using them in C++.

Functions

Swift functions can be called from C++, with some restrictions. See this table for details:

Structs

Enums

Class types

Methods

Properties

Generics

Swift standard library

This status table describes which of the following Swift standard library APIs have some experimental support for using them in C++.