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// { dg-do run }
// { dg-options "-std=gnu++0x" }
// A basic implementation of TR1's function using variadic teplates
// Contributed by Douglas Gregor <doug.gregor@gmail.com>
#include <cassert>
template<typename Signature>
class function;
template<typename R, typename... Args>
class invoker_base
{
public:
virtual ~invoker_base() { }
virtual R invoke(Args...) = 0;
virtual invoker_base* clone() = 0;
};
template<typename F, typename R, typename... Args>
class functor_invoker : public invoker_base<R, Args...>
{
public:
explicit functor_invoker(const F& f) : f(f) { }
R invoke(Args... args) { return f(args...); }
functor_invoker* clone() { return new functor_invoker(f); }
private:
F f;
};
template<typename R, typename... Args>
class function<R (Args...)> {
public:
typedef R result_type;
function() : invoker (0) { }
function(const function& other) : invoker(0) {
if (other.invoker)
invoker = other.invoker->clone();
}
template<typename F>
function(const F& f) : invoker(0) {
invoker = new functor_invoker<F, R, Args...>(f);
}
~function() {
if (invoker)
delete invoker;
}
function& operator=(const function& other) {
function(other).swap(*this);
return *this;
}
template<typename F>
function& operator=(const F& f) {
function(f).swap(*this);
return *this;
}
void swap(function& other) {
invoker_base<R, Args...>* tmp = invoker;
invoker = other.invoker;
other.invoker = tmp;
}
result_type operator()(Args... args) const {
assert(invoker);
return invoker->invoke(args...);
}
private:
invoker_base<R, Args...>* invoker;
};
struct plus {
template<typename T> T operator()(T x, T y) { return x + y; }
};
struct multiplies {
template<typename T> T operator()(T x, T y) { return x * y; }
};
int main()
{
function<int(int, int)> f1 = plus();
assert(f1(3, 5) == 8);
f1 = multiplies();
assert(f1(3, 5) == 15);
return 0;
}
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