g++4.0 diagnostic on casting a static const member initializer to a double

[Mark Mitchell]

Fariborz Jahanian wrote:
> g++ 4.0 in FSF issues a diagnostic on the following test case:
> 
> template <class T> struct S {
>   static const double scd = (double)24;
> };
> 
> test1.C:2: error: a cast to a type other than an integral or enumeration 
> type cannot appear in a constant-expression
> 
> Rewriting the above to:
> 
> template <class T> struct S {
>   static const double scd;
> };
> 
> template <class T>
> const double S<T>::scd = (double)24;
> 
> Compiles. Event though the diagnostic is clear in what it is saying, but 
> it seems to be a g++ bug
> one way or the other.

No, the input program is invalid.  From [class.static.data]:

"If  a  static  data  member  is of const integral or const enumeration 
type, its declaration in the class definition can specify a 
constant-initializer   which   shall   be   an   integral  constant 
expression(_expr.const_)."

The diagnostic could be better, but it is indeed accurate; if there's an 
initializer it must be integral constant-expression, and a cast to 
"double" cannot appear in such an expression.

-- 
Mark Mitchell
CodeSourcery, LLC
mark@codesourcery.com
(916) 791-8304