Re: [boost] [bimap][multi_index][range] sub_range vs std::pair<iter, iter>

From: shunsuke (pstade.mb_at_[hidden])
Date: 2007-05-24 20:57:22

Thorsten Ottosen wrote:
>> I sometimes expect the correct convertibility for enable_if_convertible.
>> Well, what surprised me is that msvc fails to compile
>>    value_type x = iter[c]; // 'iter[c]' returns a proxy which is convertible to value_type.
>> if value_type has such a constructor.
>>
> 
> You lost me again. There is far too little context to understand it 
> properly.

An iterator's bracket operator may return unspecified type(a.k.a. proxy)
which is convertible to its value_type.
It can be summarized as follows:

     struct A // value_type
     {
       A() { }
       template<class X> A(X x) { x.f(); } // (1)
     };

     struct B // proxy
     {
       operator A() const { return A(); } // (2)
     };

     int main() { A a = B(); }

msvc cannot compile this, preferring (1).
(I maybe found yet another msvc bug?)
So I tend to think a CopyConstructible type should implement the convertibility correctly.

Regards,

-- 
Shunsuke Sogame