On Mon, Feb 16, 2004 at 06:46:26PM +0100, Gabriel Dos Reis wrote:
David Abrahams <dave@boost-consulting.com> writes: | Gabriel Dos Reis <gdr@integrable-solutions.net> writes: | > I understand the reasoning of letting the user says what the name | > should refer to. Which makes me inclined to make the construct | > ill-formed: That is not different from the rule that says you cannot | > reclare a template-parameter in its scope. | | That would be horrible for generic code.
Care to explain why?
| What are the requirements | on the T parameter of this class template? | | template <class T> | struct Der : T | { | template <class U> | void f(U x) | {} | };
Should those requirements be different from those for
template<class S> struct Der : S { template<class U> void f(U x) { } };
Apologies ahead of time if I am putting words in anyone's mouth. I think Dave wants to imply that the class T in his example is not allowed to have a member named U according to Gaby's proposed rule. But this isn't how the rule would work; the way I see it, _these_: struct Base { typedef int U; }; template <class U> struct Derived : Base { }; // illegal struct Derived2 : Base { template <class U> void f(U u) {} // illegal }; would be illegal ("the name U already has another meaning; choose another name for your template parameter"), whereas _these_: struct Base { typedef int U; }; template <class B, class U> struct Derived : B { }; /* ... Derived<Base> ... */ template <class B> struct Derived2 : B { template <class U> void f(U u) {} }; /* ... Derived2<Base> ... */ are both fine, since Base's "U" is hidden by virtue of being a dependent name. There is still an issue of what happens if one of these last two classes issues a "using B::U" in its body; presumably then "U" ought to become outlawed as a valid template parameter name. Just my two cents here... -- -Brian McNamara (lorgon@cc.gatech.edu)