cpp/CPPlusV6/Chapter 18/wrapped1.cpp

//wrapped1.cpp -- using a function wrapper as an argument
#include <iostream>
#include <math.h>
#include <functional>
using namespace std;

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

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

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

int main()
{
    double y = 1.21;
    function<double(double)> ef1 = dub;
    function<double(double)> ef2 = sqrt;
    function<double(double)> ef3 = Fq(10.0);
    function<double(double)> ef4 = Fp(10.0);
    function<double(double)> ef5 =  [](double u) {return u*u;};
    function<double(double)> ef6 =  [](double u) {return u+u/2.0;};
    cout << "Function pointer dub:\n";
    cout << "  " << use_f(y, ef1) << endl;
    cout << "Function pointer sqrt:\n";
    cout << "  " << use_f(y, ef2) << endl;
    cout << "Function object Fp:\n";
    cout << "  " << use_f(y, ef3) << endl;
    cout << "Function object Fq:\n";
    cout << "  " << use_f(y, ef4) << endl;
    cout << "Lambda expression 1:\n";
    cout << "  " << use_f(y, ef5) << endl;
    cout << "Lambda expression 2:\n";
    cout << "  " << use_f(y,ef6) << endl;
    // cin.get();
    return 0;
}