c – const int *&vs typedef int * IntPtr

template <class T>
class A
{
    public:
        template <class X>
        void a(X *x,void (X::*fun)(const T&))
        {
        }
};

typedef int * IntPtr;

class B
{
    public:
        B() : a()
        {
            a.a(this,&B::foo); // this won't work
        }
        void foo(const int *&) // must replace `int *` here with `IntPtr`
        {
        }
        A<int *> a; // ...and here
};

class C
{
    public:
        C() : a()
        {
            a.a(this,&C::foo);
        }
        void foo(const IntPtr&)
        {
        }
        A<IntPtr> a;
};

我理解为什么typedef是有用的,但不是为什么它们是必需的. C类编译精细B没有.

这是MSVC 2008编译器的错误：

Error   1   error C2784: 'void A<T>::a(X *,void (__thiscall X::* )(const T &))' : could not deduce template argument for 'void (__thiscall X::* )(const T &)' from 'void (__thiscall B::* )(const int *&)'