Re: [boost] [Config] Patch: clang implemented N3276 decltype

Subject: Re: [boost] [Config] Patch: clang implemented N3276 decltype
From: Eric Niebler (eric_at_[hidden])
Date: 2012-03-06 23:59:24

On 3/6/2012 8:45 PM, Daniel Walker wrote:
> On Mar 6, 2012, at 11:09 PM, Eric Niebler wrote:
> 
>> On 3/6/2012 6:27 PM, Daniel Walker wrote:
>>> On Mar 6, 2012, at 9:04 PM, Eric Niebler wrote:
>>>> On 3/6/2012 5:10 PM, Michel Morin wrote:
>>>>> BTW, BOOST_NO_DECLTYPE_N3276 needs to be a more descriptive name?
>>>>
>>>> I couldn't think of a better name, and
>>>> BOOST_NO_DECLTYPE_ON_FUNCTION_CALL_EXPRESSION_FORCES_TYPE_COMPLETENESS
>>>> is too long.
>>>>
>>>> :-P
>>>
>>> How about BOOST_NO_INCOMPLETE_DECLTYPE?
>>
>> Ambiguous. Does that mean that decltype support is incomplete or that
>> decltype doesn't force type-completeness?
> 
> BOOST_NO_INCOMPLETE_DECLTYPE means the compiler does not support incomplete decltypes; i.e. it does not support decltype expressions that are incomplete types.

But that's not the issue. The issue is this:

  template<typename T> struct S {};
  template<typename T> S<T> fun(T) {}
  typedef decltype(fun(0)) Si_t; // HERE

Does the third line force the instantiation of S<int>?

Decltype works just fine on incomplete types in the simple case, so far
as I know:

  struct S;
  extern S s;
  typedef decltype(s) S_t; // OK

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com