Gabriel Dos Reis <g...@integrable-solutions.net> writes:
> On Mon, Nov 29, 2010 at 3:24 PM, Roman Kononov <ro...@xtremedata.com> wrote:
>> $ cat test.cc
>> struct X { static float const v=1; };
>>
>> $ g++ -c -std=gnu++0x test.cc
>> test.cc:1:33: error: 'constexpr' needed for in-class initialization of
>> static data member 'v' of non-integral type
>>
>> This will break a great deal of existing c++ code preventing easy
>> transition to c++0x. Maybe, the constexpr requirement should be relaxed
>> in gnu++0x mode.
>>
>> Please see the trivial patch.
>
> I believe you may be confused.
>
> Your program does not use `constexpr' at all, so I think your $SUBJECT and
> prognosis is not right. The above code is invalid C++03 code. It stays
> invalid in C++0x. However, if you do want to write something like that
> in C++0x, you do have to use `constexpr' -- that is what the diagnostic
> message is saying.
>
> Summary: this is a non-issue.
We could decide not to do anything about this, but I don't think it's a
non-issue. With -std=gnu++98 g++ accepts this invalid code. That is,
it is a g++ extension, and the code is properly rejected with
-pedantic-errors. We could decide to carry the extension forward to
-std=gnu++0x. Or we could decide to carry the extension forward to
-std=gnu++0x when -fpermissive is used. Or we could decide to just drop
the extension.
The main problem with the last option is that it complicates the
migration of existing gnu++98 programs to gnu++0x. It becomes necessary
to add constexpr to use gnu++0x. Unfortunately, gnu++98 rejects
constexpr. So there is no simple way to modify this program to be both
valid gnu++98 and valid gnu++0x. That makes the transition more
difficult.
It seems to me that it would be better for our users to accept this code
in gnu++0x mode with -fpermissive.
Ian
