Re: are these valid in c++?

From:

"Greg Herlihy" <greghe@pacbell.net>

Newsgroups:

comp.lang.c++.moderated

Date:

4 Dec 2006 15:36:05 -0500

Message-ID:

<1165250789.050314.49550@f1g2000cwa.googlegroups.com>

zade_news_cn99 wrote:

I want to define a function pointer type in my function template and use it
, just like these:

template<class InputIterator> inline
void length(InputIterator begin,InputIterator end)
  {
   typedef typename InputIterator::segment_type segment_type;
   typedef typename InputIterator::point_type point_type;
   typedef typename point_trait<point_type>::value_type point_value_type;
   typedef point_value_type (typename DistFunc*)(const segment_type&);//(1)
define a function pointer type
   DistFunc df = ...;// some value
  }

The keyword "typename" inside a template definition tells the compiler
that a particular name refers to a type (and not, say, to a variable)
defined somewhere else. And although "DistFunc" does name a type, it is
not a name defined somewhere else - but is instead defined where it
first appears inside the length() function template. Therefore the
problem is simply that this sample code has one "typename" too many:

    template <class T> class point_trait;

    template <class InputIterator>
    inline void length( InputIterator begin, InputIterator end)
    {
        typedef typename InputIterator::segment_type segment_type;
        typedef typename InputIterator::point_type point_type;
        typedef typename point_trait<point_type>::value_type
                                                      point_value_type;

        typedef point_value_type (*DistFunc)(const segment_type&);
        ...
    }

Greg

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