Skip to content

Commit fbd6946

Browse files
hyphyp
authored
Merge pull request #41816 from hyp/status-doc
[cxx-interop][docs] add a C++ interoperability status document
2 parents b183ae1 + a023cf9 commit fbd6946

File tree

1 file changed

+101
-0
lines changed

1 file changed

+101
-0
lines changed

‎docs/CppInteroperability/CppInteroperabilityStatus.md

Lines changed: 101 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,101 @@
1+
# C++ Interoperability Status
2+
3+
Swift has some experimental ability to interoperate with C++.
4+
This document provides an overview of the status of the Swift and C++ interoperability support.
5+
6+
## C++ to Swift Interoperability Status
7+
8+
Swift has the experimental ability to import a large subset of C++.
9+
This section of the document describes which C++ language and standard library features can be imported and used from Swift in an experimental manner.
10+
11+
### Importing C++
12+
13+
There are currently two experimental ways to import C++ into Swift:
14+
- **Clang modules**: can be imported into Swift. This requires a module map.
15+
- **Bridging header**: can be imported into Swift. Headers included in the bridging header will be imported.
16+
Please note that support for importing C++ 20 modules isn’t implemented.
17+
18+
Both CMake and the Swift package manager can be configured to invoke Swift with the correct arguments to import C++ headers.
19+
20+
**Note**: C++ code is imported using the Objective-C++ language mode on Apple platforms.
21+
22+
### Experimental C++ Language Support
23+
24+
This status table describes which of the following C++ language features can be used in Swift:
25+
26+
| **C++ Language Feature** | **Implemented Experimental Support For Using It In Swift** |
27+
|---------------------------------------------|---------------------------------------------------------------|
28+
| Top-level functions | Yes |
29+
| Enumerations | Yes. That includes `enum class` |
30+
| Struct / Class types | Yes - as value types, except for types without a copy constructor. Partial experimental support for importing a C++ struct/class as a reference type |
31+
| Typedefs / Type aliases | Yes |
32+
| Global Variables | Yes |
33+
| Namespaces | Yes |
34+
| Inline Namespaces | Yes, with some known issues (https://bugs.swift.org/browse/SR-15956) |
35+
| Exceptions | No |
36+
| Fields | Yes |
37+
| Member functions | Yes. Some value category overloads aren't imported |
38+
| Virtual Member Functions | No |
39+
| Operators | Yes, with some known issues |
40+
| Subscript Operators | Yes |
41+
| Constructors | Yes. That includes implicit constructors |
42+
| Destructor | Yes. C++ destructors are invoked automatically when the value is no longer used in Swift |
43+
| Copy constructor / copy assignment operator | Yes. Swift invokes the underlying copy constructor when copying a C++ value |
44+
| Move constructor / move assignment operator | No |
45+
| Base class member functions / operators | Yes, with some known issues |
46+
| Function templates | Yes |
47+
| Class templates | Yes |
48+
| Dependent types | Partially: imported as Any |
49+
| Availability Attributes | Yes |
50+
51+
52+
The following C++ code patterns or language features have specific mappings to Swift language features when imported in Swift:
53+
54+
55+
| **C++ Language Feature** | **Imported Into Swift** |
56+
|------------------------------------------------------|------------------------------------------------------------------------------------------|
57+
| `get`/`set` member functions | Imported as computed property (starting from Swift-5.7) |
58+
| `const`/non-`const` member function overload set | Both overloads are imported as a method, with non-`const` method being renamed to `mutating…` (starting from Swift-5.7). The renaming logic will change in a future version of Swift, and non-`const` methods won't be renamed |
59+
60+
61+
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.
62+
63+
64+
### C++ Standard Library Support
65+
66+
Parts of libc++ can be imported and used from Swift.
67+
68+
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.
69+
70+
| **C++ Standard Library Feature** | **Can Be Used From Swift** |
71+
|------------------------------------|----------------------------------------------|
72+
| `std::string` | Yes |
73+
| `std::vector` | Yes |
74+
75+
## Known Issues
76+
77+
### Inline Namespaces
78+
- https://bugs.swift.org/browse/SR-15956: 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/apple/swift/blob/main/test/Interop/Cxx/namespace/inline-namespace-function-call-broken.swift
79+
80+
81+
## Swift to C++ Interoperability Status
82+
83+
This section of the document describes which Swift language and standard library features can be imported and used from C++.
84+
85+
### Importing Swift
86+
87+
Swift has some experimental support for generating a header that can be imported by C++.
88+
89+
### Swift Language Support
90+
91+
This status table describes which of the following Swift language features have some experimental support for using them in C++.
92+
93+
**Functions**
94+
95+
| **Swift Language Feature** | **Implemented Experimental Support For Using It In C++** |
96+
|--------------------------------|----------------------------------------------------------|
97+
| Top-level `@_cdecl` functions | Yes |
98+
| Top-level Swift functions | Partially, only with C compatible types |
99+
| `inout` parameters | No |
100+
| Variadic parameters | No |
101+
| Multiple return values | No |

0 commit comments

Comments
 (0)