Re: [boost] Re: [OT] Hiding template parameters [was: FC++ Formal review is...]

From: Gabriel Dos Reis (gdr_at_[hidden])
Date: 2004-02-16 16:21:58

David Abrahams <dave_at_[hidden]> writes:

| Brian McNamara <lorgon_at_[hidden]> writes:
| 
| > 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.
| 
| That's what I thought he meant.

But then, your remark about "would be horrible for generic program"
is, ahem, puzzling.  You still did not explain why. 

| > 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...
| 
| OK, I think I understand now.  I think it's a bizarre and inconsistent
| rule.

What is bizarre and inconsistent about it and is not with the other
alternatives you care to name?  This question is not rhetorical.
When you register strong opinons about a technical issue or throw in
the air fashionable words like "generic  programming", the least that
could be expected is that you provide technical explanation.

|  Shall we outlaw:
| 
|   struct Base { static int x; };
| 
|   struct Derived : Base { 
|      void f(int x) {}     // Horrors! we're masking a base class member!

If you happen to pause a second and have look at the issue at hand, I'm
confident that you'll see the difference  between the case we're
discussing and your example.

|   };
| 
| Sorry for the sarcasm;

And, I'm pretty sure you know sarcasm is not appropriate for tehcnical
discussions. 

-- Gaby