Function-Template

Keywords: FunctionTemplate

This is for the readers who have basic c++ background. If you want to get the rough sketch of funtion template of c++, then there it is.

I suggest an online c++ compiler : http://coliru.stacked-crooked.com/ (You can test your simple programs on it.)

#include <iostream>
#include <functional>
#include <array>
using namespace std;

std::function<int(int)> Functional;

int TestFunc(int a){ return a;}

auto lambdaFn = [](float a)->float{ return a; };

class Functor{
 public:
    int operator()(int a){return a;}
};

class TestClass{
 public:
    int ClassMember(int a) { return a; }
    static int StaticMember(int a) { return a; }
};

int main()
{
    
    Functional = TestFunc;
    int result = Functional(10); //10
    cout << "TestFunc："<< result << endl;
    
    
    Functional = lambdaFn;
    result = Functional(22.00); //22
    cout << "Lambda："<< result << endl;
    
    
    Functor testFunctor;
    Functional = testFunctor;
    result = Functional(30); //30
    cout << "Functor："<< result << endl;
    
    
    TestClass testObj;
    Functional = std::bind(&TestClass::ClassMember, testObj, std::placeholders::_1);
    result = Functional(40); //40
    cout << "TestClass："<< result << endl;
    
    
    Functional = TestClass::StaticMember;
    result = Functional(50); //50
    cout << "TestClass(static)："<< result << endl;
    return 0;
}

function is a kind of wrapper,which provides a way to handle several funtion-like forms uniformly. If you know polymorphism, then this is easy to understand.

Let’s see another code segment.

#include <iostream>
#include <functional>
#include <map>
using namespace std;

int add(int x,int y){return x+y;}

struct divide
{
    int operator()(int denominator,int divisor)
    {
        return denominator/divisor;
    }
};

int main()
{
    
    map<char,function<int(int,int)>> op = 
    {
        {'+',add},
        {'/',divide()},
        {'-',[](int i,int j){return i-j;}}
    };
    cout << op['+'](1, 2) << endl; //3
    cout << op['-'](1, 2) << endl; //-1
    cout << op['/'](1, 2) << endl; //0
}