[cfe-commits] [libcxx] r115461 - /libcxx/trunk/include/__functional_base_03

[Howard Hinnant]

On Oct 3, 2010, at 1:01 PM, Douglas Gregor wrote:

> 
> On Oct 3, 2010, at 9:55 AM, Howard Hinnant wrote:
> 
>> On Oct 3, 2010, at 12:53 PM, Douglas Gregor wrote:
>> 
>>> 
>>> On Oct 3, 2010, at 6:59 AM, Howard Hinnant wrote:
>>> 
>>>> Author: hhinnant
>>>> Date: Sun Oct  3 08:59:56 2010
>>>> New Revision: 115461
>>>> 
>>>> URL: http://llvm.org/viewvc/llvm-project?rev=115461&view=rev
>>>> Log:
>>>> Tweak to make clang blocks work with std::functional (very fragile)
>>> 
>>> Won't we need _Block_copy calls when putting a block into a std::function, _Block_dispose when destroying that std::function, etc?
>> 
>> <shrug> I don't know.  If so then I would think it unsafe to instantiate any template with a block (not just std::function).  Such behavior doesn't follow C++ generic syntax/semantics.
> 
> IIUC, it's actually a library policy issue. My understanding is that blocks effectively capture by reference until you call _Block_copy, so when a library function accepts a block parameter it either (1) agrees to call it immediately, while the caller is still on that stack, or (2) _Block_copy the block to save a copy of the block elsewhere and run it later.
> 
> Since std::function is mainly a mechanism for "save a copy of the function object to call later", I think it makes sense to _Block_copy/_Block_dispose automatically.

Ok, I'll look into it when I have a compiler that has all of the needed language features to do the job correctly:

1.  blocks
2.  rvalue refs
3.  variadic templates.

The current function support clang is taking advantage of is nothing but a stub and destined to disappear.

-Howard