Re: [boost] providing definitions for static constants

From: Jens Maurer (Jens.Maurer_at_[hidden])
Date: 2001-04-30 16:20:03

John Maddock wrote:
> 
> >Thus, for the above example to work, you need to add
> >
> >#ifndef BOOST_NO_INCLASS_MEMBER_INITIALIZATION
> >template<class T>
> >const bool X<T>::value;
> >#endif
> >
> >to your source code.
> 
> I thought you only needed that if the value was used in a way that causes
> it's address to be taken (issue 48).

Indeed, but "taking the address" isn't meant in the specific sense
of applying operator& to it.

Here's the new wording from the proposed resolution for core issue 48:

>>> An expression is potentially evaluated unless it appears where an
>>> integral constant expression is required (see 5.19  expr.const ),
>>> is the operand of the sizeof operator (5.3.3  expr.sizeof ), or is
>>> the operand of the typeid operator and the expression does not
>>> designate an lvalue of polymorphic class type (5.2.8  expr.typeid ).

Further on, in the existing standard text, it says

>>> An object or non-overloaded function is used if its name appears
>>> in a potentially-evaluated expression.

I would take this to mean that code like

   char m = integer_traits<char>::min_val;

"uses" the object min_val and thus requires a definition for it.

Jens Maurer