当C ++使用智能指针时，C＃委托等效

Question

I am mainly a .NET programmer working on a C++ project and am trying to determine the equivalent way to handle delegates that use the Action and Function template types. I use the delegates both as events and callbacks within the .NET code. My C++ project uses smart pointers and the same delegate design patterns as a C# program would. What is the best way to handle this situation? It is not clear to me how to pass and maintain a function pointer that also keeps track of the smart pointer and potentially the deletion of the underlying object since the event container uses a weak reference. The library needs to be multi-platform so using CLR is unfortunately not an option.

Answer 1

What you are looking for is a method pointer bound to an existing object, that's it ?

The you should have a look for boost::bind . If your environment supports it, you can also use std::tr1::bind or even std::bind if it supports C++11.

The example which illustrates what you want is :

struct X
{
    bool f(int a);
};
X x;
shared_ptr<X> p(new X);
int i = 5;

bind(&X::f, ref(x), _1)(i);     // x.f(i)
bind(&X::f, &x, _1)(i);         //(&x)->f(i)
bind(&X::f, x, _1)(i);          // (internal copy of x).f(i)
bind(&X::f, p, _1)(i);          // (internal copy of p)->f(i)

The last two examples are interesting in that they produce "self-contained" function objects. bind(&X::f, x, _1) stores a copy of x. bind(&X::f, p, _1) stores a copy of p, and since p is a boost::shared_ptr, the function object retains a reference to its instance of X and will remain valid even when p goes out of scope or is reset().

For the differences between boost::bind , std::tr1::bind and std::bind , I let you see this other question on SO.

Answer 2

Take a look at: http://www.codeproject.com/Articles/7150/Member-Function-Pointers-and-the-Fastest-Possible

It will also explain why delegates in C++ are a little tricky. This library was recommend in a game development book i read (So i'm assuming its very fast).