c++使用functional装饰函数模板，不用创建多个实例对象

#include<iostream>
#include<functional>

template<typename T>
T use_f(T v, std::function<T(T)> f)
{
	static int count = 0;
	count += 1;
	std::cout << " use_f count = " << count
		<< ", &count="<< &count << std::endl;
	return f(v);
}

double dub(double x) { return 2.0 * x; }


class Fq
{
private:
	double z_;
public:
	Fq(double z = 1.0) :z_(z) {}
	double operator()(double q) { return z_ + q; }
};

int main()
{
	double y = 1.21;
	std::cout << " " << use_f<double>(y, dub);
	std::cout << " " << use_f<double>(y, Fq(10.0));

	return 0;
}

可以看到地址是一样的，不同的函数没有另外创建对象