[Patch, libstdc++/68877] Reimplement __is_[nothrow_]swappable

[Daniel Krügler]

This is a second try for a patch for libstdc++ bug 68877. See below
for responses.

2015-12-22 22:42 GMT+01:00 Jonathan Wakely <jwakely@redhat.com>:
> On 21/12/15 12:45 +0100, Daniel Krügler wrote:
>>
>> 2015-12-14 21:48 GMT+01:00 Daniel Krügler <daniel.kruegler@gmail.com>:
>>>
>>> This is a reimplementation of __is_swappable and
>>> __is_nothrow_swappable according to
>>>
>>> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4511.html
>>>
>>> and also adds a missing usage of __is_nothrow_swappable in the swap
>>> overload for arrays. Strictly speaking the latter change differs from
>>> the Standard specification which requires the expression
>>> noexcept(swap(*a, *b)) to be used. On the other hand the Standard is
>>> broken in this regard, as pointed out by
>>>
>>> http://cplusplus.github.io/LWG/lwg-active.html#2554
>
> The patch doesn't apply cleanly because it repeats some of the new
> files either twice or three times (and also has some trailing
> whitespace that shouldn't be there).

I can confirm this, albeit I don't understand why this happens. I'm
using TortoiseSVN and when trying to create a patch file it creates
double entries for new directories. I have now explicitly removed the
added directories from the patch, I hope that your patch experience is
now better.

> After fixing the patch to only
> create new files once it applies, but then I get some FAILs:
>
> FAIL: 20_util/is_nothrow_swappable/value.cc (test for excess errors)
> FAIL: 20_util/is_swappable/value.cc (test for excess errors)
>
> I don't have time to analyse these today, so I'll wait until you're
> able to do so.

I'm sorry for these errors. I could now find a way to reproduce the
tests and found that they were partially due to an incomplete commit
and partially because of sleepiness on my side. I hopefully fixed
these blatant errors and took the chance to increase the test cases
even further.

Thanks again,

- Daniel
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2015-12-23  Daniel Kruegler  <daniel.kruegler@gmail.com>

    PR libstdc++/68877
    * include/std/type_traits: Following N4511, reimplement __is_swappable and
    __is_nothrow_swappable. Move __is_swappable to namespace std, adjust
    callers. Use __is_nothrow_swappable in swap.
    * include/bits/move.h: Use __is_nothrow_swappable in swap.
    * testsuite/20_util/is_nothrow_swappable/value.cc: Extend; remove 
    __is_swappable related tests.
    * testsuite/20_util/is_swappable/value.cc: New.
    * testsuite/20_util/is_swappable/requirements/explicit_instantiation.cc: 
    New.
    * testsuite/20_util/is_swappable/requirements/typedefs.cc: New.
    * testsuite/25_algorithms/swap/68877.cc: New.
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