[cfe-dev] libcxx: std::function should be able to capture blocks

[David Blaikie]

[+Marshall as libc++ maintainer]

What would it look like if we just provided a value-semantic-C++ wrapper
around blocks, translating C++ move/copy operations down to the
Block_copy/release/etc operations?

That way it'd be orthogonal to the type erasure of std::function and could
be used just for a convenience when using blocks in C++ code anyway:

  auto x = make_cpp_block(/* block stuff */);
  auto y = x;
  x();
  etc...

(& then you'd compose them with "std::function<...> f =
make_cpp_block(...);" (the block wrapper could have an implicit conversion
to std::function))

It's a little more text, but doesn't require an extension to the standard
library, and can be used independently.

On Wed, Oct 1, 2014 at 11:38 AM, Jared Grubb <jared.grubb at gmail.com> wrote:

> == Background:
> std::function will wrap anything that is callable (and can be
> copied/moved). Blocks are copyable and callable, however you need to use
> the reference counting Block_copy/Block_release functions.
>
> == Request for Comment on the Patch:
> I am working on a patch that will allow std::function to capture blocks
> correctly (under the right feature guards).
>
> Functionally, the patch is complete. However, it's not checkin-ready as I
> had a couple questions on the approach:
>  * Is the approach right? I specialized the __func storage class, as that
> seems to be the right thing to customize.
>  * I have included some unit test implementations. There are quite a few
> std::function unit tests, so I wanted to make sure I was on the right track
> before I do all of them.
>  * Should I add tests for ObjC++ code, under ARC and non-ARC scenarios?
> There are no ObjC++ files in libcxx, and the test-runner does not yet
> support them. Adding this is not hard, but it's a change in how things are
> today.
>
> If this looks like it's on the right track, I will flush out the rest of
> the unit tests, and optionally add ObjC++ unit tests.
>
>
>
>
> Jared
>
>
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>
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