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

[Douglas Gregor]

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.

	- Doug
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