Re: C++ PATCH: PR 24389

[Gabriel Dos Reis <gdr@integrable-solutions.net>]

Mark Mitchell <mark@codesourcery.com> writes:

| This patch fixes PR c++/24389, which was (yet more) fallout from the
| static data member patch.  The problem here was not, as stated in the
| PR, that we were giving X<0>::n_primes non-weak linkage, but rather
| that we are emitting a definition for X<I>::n_primes, where I was a
| non-type template parameter!  
| 
| The cause was that the C++ standard, in its infinite wisdom, makes a
| non-static data member in a class template non-dependent within the
| scope of that template, so that, for example:
| 
|    template <typename T>
|    struct S {  
|      static const int I = 7; // I is not value-dependent within S<T>
|      void f() { 
|        A<I>::type t; // No "typename" keyword required; this is A<7>. 
|      }
|    };
| 
| As a result, we must play funny games with non-static data members,
| even though we generally never evaluate expressions within
| uninstantiated templates.  In particular, within integral constant
| expressions, we must fold non-dependent expressions.

That was new in C++03, compared to C++98, in search of rule optimizations
in small.  I'm glad we share similar appreciationsof list of special rules
and optimization in small ;-)

-- Gaby