If you read the boost::any documentation they provide the source for the idea: http://www.two-sdg.demon.co.uk/curbralan/papers/ValuedConversions.pdf
It’s basic information hiding, an essential C++ skill to have. Learn it!
Since the highest voted answer here is totally incorrect, and I have my doubts that people will actually go look at the source to verify that fact, here’s a basic implementation of an any like interface that will wrap any type with an f() function and allow it to be called:
struct f_any
{
f_any() : ptr() {}
~f_any() { delete ptr; }
bool valid() const { return ptr != 0; }
void f() { assert(ptr); ptr->f(); }
struct placeholder
{
virtual ~placeholder() {}
virtual void f() const = 0;
};
template < typename T >
struct impl : placeholder
{
impl(T const& t) : val(t) {}
void f() const { val.f(); }
T val;
};
// ptr can now point to the entire family of
// struct types generated from impl<T>
placeholder * ptr;
template < typename T >
f_any(T const& t) : ptr(new impl<T>(t)) {}
// assignment, etc...
};
boost::any does the same basic thing except that f() actually returns typeinfo const&
and provides other information access to the any_cast function to work.