Re: Dependent type in template base class

From:

cbarron3@ix.netcom.com (Carl Barron)

Newsgroups:

comp.lang.c++.moderated

Date:

13 Jan 2007 04:46:23 -0500

Message-ID:

<1hru1uf.1arci7n1ud5d4mN%cbarron3@ix.netcom.com>

Stephan Tolksdorf <andorxor@gmx.de> wrote:

Carl Barron wrote:

   is
   template <class T>
   class test:public base<T> // is private inheritance really wanted??
   {
      typedef typename base<T>::param_type param_type;
      test(param_type &p);
   };

   any better??

Thanks for your reply.

Private or public inheritance doesn't matter for exemplifying the
problem (and all the members in the example are private anyway).

Using the typedef instead of the using declaration was my proposal, too.
It seems to work flawlessly. My question is whether I have to expect any
subtle problems due to the introduction of a new name through the
typedef. Otherwise the typedef and using declaration seem to be quite
equivalent.

Stephan

  Well base<T> is not examined when test<T> is declared, only when it is
instanced. Therefore the declaration of test<T> knows little about
base<T>. The typedef tells the compiler param_type is a type, using
does not, as using can be used with types, data members or member
functions. Thats the difference.

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