no-reply@allegro.cc (Martin Kalbfuß) — Thu, 26 Aug 2010 14:38:08 +0000

I try to pass a function type as template parameter. It's the first time I do this, and I'm not really surprised that it isn't working.

#SelectExpand
  1#pragma once
  2
  3#include 
  4
  5template <typename T, typename Dtor=void(T*)>
  6class ResourceManager
  7{
  8  typedef typename std::map<T*, Dtor> Resources;
  9  typedef typename Resources::iterator Iterator;
 10
 11private:
 12  Resources resources;
 13
 14public:
 15  ResourceManager();
 16  ~ResourceManager();
 17  void add_resource(T *resource, Dtor dtor);
 18  void del_resource(T *resource);
 19};
 20
 21template <typename T, typename Dtor>
 22ResourceManager<T, Dtor>::ResourceManager() {};
 23
 24template <typename T, typename Dtor>
 25void ResourceManager<T, Dtor>::add_resource(T *resource, Dtor dtor)
 26{
 27  resources[resource] = dtor;
 28}
 29
 30template <typename T, typename Dtor>
 31void ResourceManager<T, Dtor>::del_resource(T *resource)
 32{
 33  Iterator it = resources.find(resource);
 34  if(it != resources.end())
 35    {
 36      (*it).second(resource);
 37      resources.erase(it);
 38    }
 39}
 40
 41template <typename T, typename Dtor>
 42ResourceManager<T, Dtor>::~ResourceManager()
 43{
 44  for(Iterator it = resources.begin(); it != resources.end(); it++)
 45    (*it).second((*it).first);
 46
 47  resources.clear();
 48}

error: field 'std::pair<_SDL_TimerID* const, SDL_bool ()(_SDL_TimerID*)>::second' invalidly declared function type

What's the right way to do it?

Thanks.

Martin

Edit:

Oh no. . I missed the (*). Problem solved. But with boost::function it is any_type(any_type). How do they do this ?

no-reply@allegro.cc (axilmar) — Thu, 26 Aug 2010 16:56:55 +0000

Quote:

How do they do this ?

Example:

#SelectExpand
  1//template prototype
  2template <class T> class Foo {
  3};
  4
  5//specialization for function with 0 params
  6template <class R> class Foo<R()> {
  7};
  8
  9//specialization for function with 1 param
 10template <class R, class T1> class Foo<R(T1)> {
 11};
 12
 13//specialization for function with 2 params
 14template <class R, class T1, class T2> class Foo<R(T1, T2)> {
 15};

no-reply@allegro.cc (anonymous) — Thu, 26 Aug 2010 23:27:19 +0000

In this case that would amount to:

namespace std {
template <class T, class U>
struct pair<T, void(U*)>
{
    T first;
    void (*second)(U*);
};
}

Would not recommend, even if adding the specialization is legal according to the standard (?).

Problem with function template parameter and std::pair