Re: Partial specialisation

From:
Alan Woodland <ajw05@aber.ac.uk>
Newsgroups:
comp.lang.c++
Date:
Fri, 18 May 2007 11:06:22 +0100
Message-ID:
<1179483777.290142@leri.aber.ac.uk>
Victor Bazarov wrote:

siddhu wrote:

On May 17, 9:10 am, Alan Woodland <a...@aber.ac.uk> wrote:

[snip]

Is there a valid way to achieve this without using a non member
template function and calling that from within the generic doStuff()?

Thanks,
Alan

You can not specialize the method but you can specialize the class.
Try this.

template <typename T>
class Foo<T,Bar<T> > {
public:
  void doStuff();
};

template <typename T>
void Foo<T, Bar<T> >::doStuff() {
  std::cout << "Specific" << std::endl;

}


This is usually a problem if the need is to [partially] specialise
a single member function out of dozens. Having to specialise the
entire class template means you need to repeat all but one functions
and give them /exactly same/ implementation as the non-specialised
template.


For reference the solution I went with in the end was:

#include <iostream>

template <typename T>
class Bar {
};

template <typename T, typename P>
class DoStuffImpl {
public:
   static void apply() {
      std::cout << "General" << std::endl;
   }
};

template <typename T>
class DoStuffImpl<T, Bar<T> > {
public:
   static void apply() {
      std::cout << "Specific" << std::endl;
   }
};

template <typename T, typename P>
class Foo {
public:
   void doStuff();
};

template <typename T, typename P>
void Foo<T, P>::doStuff() {
   DoStuffImpl<T, P>::apply();
}

int main() {
   Foo<float, Bar<float> > a;
   a.doStuff();

   Foo<float, float> b;
   b.doStuff();

   return 0;
}

Which does what I wanted (i.e. not having to repeat all the other
members) via an additional level of indirection (that probably can be
optimised by a decent compiler anyway)

Thanks,
Alan

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