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egorzhdan merged 6 commits into from
Apr 8, 2025
Merged

[cxx-interop] Document features that shipped in 6.1 and earlier #956

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3d80633
[cxx-interop] Document virtual method support
egorzhdan Apr 3, 2025
3058de9
[cxx-interop] Document `std::unique_ptr` support
egorzhdan Apr 3, 2025
9eb5298
[cxx-interop] Update stale link to known issues
egorzhdan Apr 3, 2025
cb8b6f9
[cxx-interop] Document `char8_t` support
egorzhdan Apr 3, 2025
9818950
[cxx-interop] Document nested struct support
egorzhdan Apr 4, 2025
0ef4b53
[cxx-interop] Update revision history
egorzhdan Apr 7, 2025
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21 changes: 15 additions & 6 deletions documentation/cxx-interop/index.md
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Expand Up @@ -492,7 +492,8 @@ because they return a reference that points into the `Forest` object.

#### Virtual Member Functions

Currently virtual member functions are not available in Swift.
Virtual methods of C++ value types cannot be called from Swift. This is similar
to C++, where you can only call virtual methods on a pointer or a reference.

#### Static Member Functions

Expand Down Expand Up @@ -1254,6 +1255,14 @@ object.doSomething()
// `object` will be released here.
```

### Inheritance and Virtual Member Functions

Similar to value types, casting an instance of a derived reference type to a
base reference type, or vice versa, is not yet supported by Swift.

If a reference type has virtual methods, you can call those methods from Swift.
This includes pure virtual methods.

#### Exposing C++ Shared Reference Types back from Swift

C++ can call into Swift APIs that take or return C++ Shared Reference Types. Objects of these types are always created on the C++ side,
Expand All @@ -1276,11 +1285,6 @@ The C++ caller of this function is responsible for releasing the object.
The `SWIFT_UNSAFE_REFERENCE` annotation macro has the same effect as `SWIFT_IMMORTAL_REFERENCE`
annotation macro. However, it communicates different semantics: the type is intended to be used unsafely, rather than living for the duration of the program.

### Unique Reference Types

Unique reference types, such as types passed around by `std::unique_ptr` are
not yet supported by Swift.

## Using C++ Standard Library from Swift

This section describes how to import the C++ standard library, and how
Expand Down Expand Up @@ -1982,6 +1986,11 @@ that are outlined in the documentation above.

This section lists the recent changes made to this reference guide.

**2025-04-07**

- C++ virtual methods of reference types are now available in Swift.
- `std::unique_ptr` is now supported in Swift.

**2024-08-12**

- Added several customization macros from `<swift/bridging>` to the list.
Expand Down
16 changes: 7 additions & 9 deletions documentation/cxx-interop/status/index.md
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Expand Up @@ -196,10 +196,11 @@ The following C++ standard library types are supported in Swift:
- Specializations of `std::set`, `std::multiset` and `std::unordered_set`
- Specializations of `std::optional`
- Specializations of `std::shared_ptr`
- Specializations of `std::unique_ptr`
- Specializations of `std::array`

Other standard library types, like `std::unique_ptr`, `std::function` and
`std::variant` are not yet supported in Swift.
Other standard library types, like `std::function` and `std::variant`, are not
yet supported in Swift.

### Other C++ Features Handled by Swift

Expand Down Expand Up @@ -229,16 +230,14 @@ header.

### Swift Structures Supported by C++

Swift can generate C++ representation for most top-level Swift structures. The
following Swift structures are not yet supported:
Swift can generate C++ representation for most Swift structures. The following
Swift structures are not yet supported:

- Zero-sized structures that don't have any stored properties
- Non-copyable structures
- Generic structures with generic constraints, or with more than three generic
parameters, or that have variadic generics

Swift currently does not expose nested structures to C++.

### Swift Classes and Actors Supported by C++

Swift can generate C++ representation for most top-level Swift classes and
Expand All @@ -247,8 +246,6 @@ following Swift classes are not yet supported:

- Generic classes and actors

Swift currently does not expose nested classes and actors to C++.

### Swift Enumerations Supported by C++

Swift can generate C++ representation for most top-level Swift enumerations
Expand Down Expand Up @@ -351,6 +348,7 @@ standard library that can be represented in C++:
| `CBool` | `bool` |
| `CChar` | `char` |
| `CWideChar` | `wchar_t` |
| `CChar8` | `char8_t` |
| `CChar16` | `char16_t` |
| `CChar32` | `char32_t` |
| `CSignedChar` | `signed char` |
Expand All @@ -369,7 +367,7 @@ standard library that can be represented in C++:
## Constraints and Limitations

Swift has some known limitations related to C++ interoperability support.
They're currently [listed on GitHub](https://github.com/swiftlang/swift/issues/66159).
They are currently [tracked on GitHub](https://github.com/swiftlang/swift/issues?q=is%3Aissue%20state%3Aopen%20label%3A%22c%2B%2B%20interop%22).

### Swift Package Manager Constraints

Expand Down