Re: [Boost-users] [partly: Boost.Function] typesafe (templated) wrapper around class with void* API

29 Jan 2009


      AMDG

Christoph Duelli wrote:
...
template<typename T>
class B : public A
{
public:
   void do_something(T* t) { A::do_something(t); }
protected:
   // Force user to provide a correctly typed callback.
   virtual bool help_me(const T*) =0;
private:
   // call the user's safe callback
   bool help_me(const void* t)
   {
      return help_me(static_cast(t));
   }
};
More specific questions:
i) I assume the penalty for my callback "help_me" is one
more indirection. Can't see that optimized away.
Use CRTP

template
class B {
private:
    bool help_me(const void* t) {
        return static_cast(this)->help_me(static_cast(t));
    }
};
...
ii) Assuming A's interface gets passed a real callback
function (a Boost.Function) instead:
class A
{
public:
   typedef boost::function helper_func;
   void do_something(void*, helper_func);
};
is it somehow possible to get a typesafe templated B such that
template<typename T>
class B : public A
{
public:
   typedef boost::function helper_func;
   void do_something(T* t, helper_func hf)
   {
      // this makes my compiler unhappy (when instanced).
      // I do understand that... can it be worked around somehow?
      A::do_something(t, hf);
   }
};
A::do_something(t, boost::lambda::bind(hf, 
boost::lambda::ll_static_cast(boost::lambda::_1)));

In Christ,
Steven Watanabe