#ifndef SCREEN_H
#define SCREEN_H

#include <string>

class Screen {
public:
    typedef std::string::size_type pos;

    // Action is a type that can point to a member function of Screen
    // that returns a reference to a Screen and takes no arguments
    using Action = Screen&(Screen::*)();

    // constructor: build screen of given size containing all blanks
    Screen(pos ht = 0, pos wd = 0): contents(ht * wd, ‘ ‘), cursor(0), 
                                    height(ht), width(wd) { }
    friend int main();
    // data is a static member that returns a pointer to member
    static const std::string Screen::*data() 
     { return &Screen::contents; }

    char get_cursor() const { return contents[cursor]; }
    char get() const { return contents[cursor]; }
    inline char get(pos ht, pos wd) const;
private:
    std::string contents;
    pos cursor;
    pos height, width;

public:
    // cursor movement functions 
    // beware: these functions don‘t check whether the operation is valid
    Screen& home() { cursor = 0; return *this; }
    Screen& forward() { ++cursor; return *this; }
    Screen& back() { --cursor; return *this; }
    Screen& up() { cursor += height; return *this; }
    Screen& down() {cursor -= height; return *this; }

    // specify which direction to move; enum see XREF(enums)
    enum Directions { HOME, FORWARD, BACK, UP, DOWN };
    Screen& move(Directions);
private:
    static Action Menu[];      // function table
};

char Screen::get(pos r, pos c) const // declared as inline in the class
{
    pos row = r * width;      // compute row location
    return contents[row + c]; // return character at the given column
}

inline
Screen& Screen::move(Directions cm)
{
    // run the element indexed by cm on this object
    return (this->*Menu[cm])(); // Menu[cm] points to a member function
}

#endif

#include "Screen.h"

Screen::Action Screen::Menu[] = { &Screen::home,
                                  &Screen::forward,
                                  &Screen::back,
                                  &Screen::up,
                                  &Screen::down,
                                };

#include "Screen.h"

#include <functional>
using std::function; 

#include <iostream>
using std::cout; using std::endl;

#include <string>
using std::string;

struct X {
    int foo(int i) { cout << "foo(" << i << ")" << endl; return i; }
};

void xfcn()
{
    function<int (X*, int)> f;
    f = &X::foo;        // pointer to member

    X x;
    int v = f(&x, 5);
    cout << "v = " << v << endl;
}

int main ()
{
    // pdata can point to a string member of a const (or nonconst) Screen
    const string Screen::*pdata;  // uninitialized
    pdata = http://www.mamicode.com/&Screen::contents;    // points to the contents member
    auto pdata2 = &Screen::contents; // equivalent declaration

    // data() returns a pointer to the contents member of class Screen
    const string Screen::*pdata3 = Screen::data();
    
    // Screen objects
    Screen myScreen, *pScreen = &myScreen;
    const Screen cScreen, *pcScreen = &cScreen;

    // .* dereferences pdata to fetch the contents member 
    // from the object myScreen
    auto str = myScreen.*pdata;  // s is a string
    auto cstr = cScreen.*pdata;  // c is a const string
    
    // ->* dereferences pdata to fetch contents 
    // from the object to which pScreen points
    str = pScreen->*pdata;  
    
    // pmf is a pointer that can point to a Screen member function 
    // that takes no arguments, returns a char, and is const
    // that returns a char and takes no arguments
    auto pmf = &Screen::get_cursor;
    char (Screen::*pmf2)() const = &Screen::get; // same type as pmf
    
    pmf = &Screen::get; // which version of get deduced from type of pmf
    pmf2 = &Screen::get_cursor;
    
    Screen s;
    char c1 = s.get_cursor(); // gets character at the cursor directly
    char c2 = (s.*pmf2)();    // calls get_cursor indirectly through pmf2
    
    // call the function to which pmf points 
    // on the object to which pScreen points
    c1 = (pScreen->*pmf)();  
    
    // pmf3 points to the two-parameter version of get
    char (Screen::*pmf3)(Screen::pos, Screen::pos) const = &Screen::get;
    c1 = myScreen.get(0,0);     // call two-parameter version of get 
    c2 = (myScreen.*pmf3)(0,0); // equivalent call to get
    
    // Op is a type that can point to a member function of Screen 
    // that returns a char and takes two pos arguments
    using Op = char (Screen::*)(Screen::pos, Screen::pos) const;
    // equivalent declaration of Op using a typedef
    typedef char (Screen::*Op)(Screen::pos, Screen::pos) const;

    Op get = &Screen::get; // get points to the get member of Screen
    
    myScreen.move(Screen::HOME);  // invokes myScreen.home
    myScreen.move(Screen::DOWN);  // invokes myScreen.down

    // bind an object of type function to a pointer to member
    function<char (const Screen*)> f = &Screen::get_cursor;

    return 0;
}