[cfe-dev] [PATCH] Add APValue::swap

[Daniel Dunbar]

On Thu, Mar 8, 2012 at 3:05 PM, Benjamin Kramer
<benny.kra at googlemail.com> wrote:
>
> On 08.03.2012, at 23:54, David Blaikie wrote:
>
>> On Thu, Mar 8, 2012 at 2:46 PM, Chris Lattner <clattner at apple.com> wrote:
>>>
>>> On Mar 8, 2012, at 10:45 AM, Howard Hinnant wrote:
>>>
>>>> On Mar 8, 2012, at 1:39 PM, Daniel Dunbar wrote:
>>>>
>>>>> I wanted to make the copy assignment operator private to encourage
>>>>> callers to see if they could use swap instead.
>>>>>
>>>>> My motivation here seems confused though, per subsequent discussion.
>>>>
>>>> I think you're just ahead of your time.  Sounds like you're trying to encourage C++11 move assignment. :-) (which I think would be a very good idea, but requires commitment to using C++11)
>>>
>>> I think that it would be completely reasonable (maybe even, "insanely great"?) to put move constructors and assignment operators into llvm & clang if they help performance and are *optional* and ifdef'd on compiler support.
>>>
>>> That would just mean that people with c++'11 compilers can get better build times, but that we remain compatible with older compilers.
>>
>> Usually we have to/have worked around the cases (you know, the usual
>> "don't return big things by value") - the most common things that
>> would benefit would be stuff that this already happens for (eg:
>> std::string). Anyone know of good candidates that we wouldn't
>> reasonably fix for the 98 case by removing the copies?
>
> We have some cases of SmallVectors and DenseMaps of objects with non-trivial copy ctors. It would spare us a few deep copies if the container would move them when it reallocates.
>
> Not sure if it's worth introducing a ton of #ifdef'd code. Sounds like a maintenance nightmare to me.

I agree. It's also a testing nightmare, I'd hate to have another way
for "it worked for me".

 - Daniel

>
> - Ben
>
>>
>> - David
>>
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