[cxx-interop] Add SWIFT_RETUNRS_(UN)RETAINED discussions to C++ interop docs #1077
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I had some comments inline. cc @egorzhdan just in case he also wants to take a look.
| @@ -1255,6 +1255,30 @@ object.doSomething() | |||
| // `object` will be released here. | |||
| ``` | |||
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| To specify the ownership of returned `SWIFT_SHARED_REFERENCE` types, use the `SWIFT_RETURNS_RETAINED` and `SWIFT_RETURNS_UNRETAINED` annotations on C++ functions and methods. These annotations tell the Swift compiler whether the type is returned as `+1` (retained) or `+0` (unretained). This is necessary to ensure that appropriate `retain`/`release` operations are inserted at the boundary: | |||
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Would these annotations work on C, and Objective-C code? If yes, maybe we should not emphasize C++ here (also this is the C++ interop documentation so this might be redundant information anyway.)
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| let unowned = makeUnownedObject() | ||
| unowned.doSomething() | ||
| // make sure `unowned` remains valid while in use |
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Wouldn't Swift automatically increase reference counting operations to guarantee that unowned is valid? I think we should check with someone if we are unsure before adding this to the documentation.
| // make sure `unowned` remains valid while in use | ||
| ``` | ||
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| These ownership annotations are also supported in Objective-C or Objective-C++ functions that return C++ `SWIFT_SHARED_REFERENCE` types. |
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Is it possible for an Objective-C function to return a C++ type? Isn't that already Objective-C++?
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| These ownership annotations are also supported in Objective-C or Objective-C++ functions that return C++ `SWIFT_SHARED_REFERENCE` types. | ||
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Is the default ownership convention documented somewhere? If not, this might be a good place to add.
Documenting the usage of
SWIFT_RETUNRS_(UN)RETAINEDannotations to specify the ownership convention of the returnedSWIFT_SHARED_REFERENCEtypes from C++ functions and methodsrdar://116817243