[cfe-commits] [PATCH] Suggested rewording for lamba return values

Aaron Ballman aaron at aaronballman.com
Fri Jun 1 17:36:12 PDT 2012


On Mon, May 28, 2012 at 6:33 PM, Aaron Ballman <aaron at aaronballman.com> wrote:
> On Thu, May 24, 2012 at 10:36 AM, Aaron Ballman <aaron at aaronballman.com> wrote:
>> On Thu, May 24, 2012 at 12:50 AM, Richard Smith <richard at metafoo.co.uk> wrote:
>>> On Tue, May 22, 2012 at 6:54 PM, Aaron Ballman <aaron at aaronballman.com>
>>> wrote:
>>>> When a lambda expression omits the return type information, the
>>>> standard requires the lambda statement body to be a single return
>>>> statement.  However, as a language extension, we (and several other
>>>> compilers) support determining the return type if all of the
>>>> function's return types agree.
>>>> The problem is, the wording for the warning we emit is a bit difficult
>>>> to parse.  It's a semantically correct statement, but it's not
>>>> immediately obvious what the problem is or how to rectify it.
>>>> Consider:
>>>> auto i = []() { static const int foo = 12; return &foo; }();
>>>> This will emit a diagnostic that says "C++11 requires lambda with
>>>> omitted result type to consist of a single return statement" --
>>>> however, a likely initial response to this is "but I do only have a
>>>> single return statement!"
>>>> This patch rewords the diagnostic to be a bit more clear (hopefully):
>>>> "C++11 requires a lambda expression with omitted result type to
>>>> consist solely of a return statement"
>>>> Thoughts?
>>> I would be in favor of removing the warning entirely, now that Clang 3.1 has
>>> shipped. The C++ core working group has already agreed that this should be
>>> allowed. It's currently under consideration by the evolution working group,
>>> whom I think are unlikely to say no -- and if they do, we will have time to
>>> react before 3.2 is released.
>> That would certainly work as well -- is there a general preference one
>> way or the other?
>> ~Aaron
> Here is a patch that removes the warning entirely as per Richard's
> suggestion -- any objections?
> ~Aaron

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