Brian McNamara <lorgon@cc.gatech.edu> writes: | 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. The base class "T" is dependent, therefore it is not examined during parsing; therefore, it has nothing to say about "U". | 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 Agreed. | 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"), Agreed. | 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. Again, agreed. | 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. Yes, because they're (alias) declarations of "U". | Just my two cents here... Thanks. They're appreciated. -- Gaby