hiding of template parameter of member template

问题

from temp.local :

In the definition of a member of a class template that appears outside of the class template definition, the name of a member of the class template hides the name of a template-parameter of any enclosing class templates (but not a template-parameter of the member if the member is a class or function template). [ Example:

template<class T> struct A {
  struct B { /* ... */ };
  typedef void C;
  void f();
  template<class U> void g(U);
};

template<class B> void A<B>::f() {
  B b;              // A's B, not the template parameter
}

template<class B> template<class C> void A<B>::g(C) {
  B b;              // A's B, not the template parameter
  C c;              // the template parameter C, not A's C
}

— end example ]

the problem is that, each compiler, that i have tried ( g++, vc, icc, clang ), treats C in A<B>::g(C) as A's member name and doesn't compile that example.

Is this a common bug.?

回答1:

While the link you gave appears to be a draft and explicitly states it is not a part of any standard (http://eel.is/c++draft/), this particular clause in the draft appears to be identical to ISO C++ 14.6.1, paragraph 7.

So it does indeed seem to be either a common compiler bug or a clause that conflicts with and lost out to other clauses. I verified the example doesn't compile on MacOS Clang v802.0.42). Since you say all the major compilers emit errors here, I would suspect this clause is not reasonable to implement due to conflicts with some other clause(s).

EDIT: I also found a discussion within the standards community here related to this topic. The depth with which it gets discussed here suggests to me that this rule is contentious and may even be changed.

来源：https://stackoverflow.com/questions/41313565/hiding-of-template-parameter-of-member-template