Digital Mars - D.gnu - D noob question

↑ ↓ ← → John Love-Jensen <love-jensen mchsi.com> writes:

Hi everyone,

I'm new to D Programming Language.

I was wondering how one would code the following (see below) C++ code in D.

Some of the paradigms in particular:
+ using the assignment operator as the setter
+ using the cast operator as the getter
+ working with the output system to print the object's state

This part in D is easy...
typedef int X;
typedef int Y;
...I wish C++ had actually typing typedef instead of mere aliasing typedef.

The assignment-setter paradigm and the cast-getter paradigm are less 
clear to me for how to do them in D.

I have no clue how to incorporate Point with import std.stdio's writef.

Thanks,
--Eljay

- - - - - - - - - - - - - - - - - - -

#include <iostream>

using std::cout;
using std::endl;
using std::ostream;

class X
{
     int m;
public:
     explicit X(int in) : m(in) { }
     X() : m(0) { }
     operator int () const { return m; }
};

class Y
{
     int m;
public:
     Y() : m(0) { }
     explicit Y(int in) : m(in) { }
     operator int () const { return m; }
};

class Point
{
     X x;
     Y y;
public:
     Point(X inX, Y inY) : x(inX), y(inY) { }
     Point() { }
     void operator = (X inX) { x = inX; }
     void operator = (Y inY) { y = inY; }
     operator X () const { return x; }
     operator Y () const { return y; }
};

ostream& operator << (ostream& output, Point const& point)
{
     output << X(point) << "," << Y(point);
     return output;
}

int main()
{
     Point point;
     X x;
     Y y;
     x = X(17);
     cout << "point: " << point << "\nx    : " << x << "\ny    : " << y 
<< endl;
     point = x;
     point = Y(33);
     y = point;
     cout << "point: " << point << "\nx    : " << x << "\ny    : " << y 
<< endl;
}

Aug 21 2005

↑ ↓ ← → Derek Parnell <derek psych.ward> writes:

On Sun, 21 Aug 2005 14:29:43 -0500, John Love-Jensen wrote:

 Hi everyone,
 
 I'm new to D Programming Language.
 
 I was wondering how one would code the following (see below) C++ code in D.
 
 Some of the paradigms in particular:
 + using the assignment operator as the setter
 + using the cast operator as the getter
 + working with the output system to print the object's state
 
 This part in D is easy...
 typedef int X;
 typedef int Y;
 ...I wish C++ had actually typing typedef instead of mere aliasing typedef.
 
 The assignment-setter paradigm and the cast-getter paradigm are less 
 clear to me for how to do them in D.
 
 I have no clue how to incorporate Point with import std.stdio's writef.
 
 Thanks,
 --Eljay
 
 - - - - - - - - - - - - - - - - - - -
 
 #include <iostream>
 
 using std::cout;
 using std::endl;
 using std::ostream;
 
 class X
 {
      int m;
 public:
      explicit X(int in) : m(in) { }
      X() : m(0) { }
      operator int () const { return m; }
 };
 
 class Y
 {
      int m;
 public:
      Y() : m(0) { }
      explicit Y(int in) : m(in) { }
      operator int () const { return m; }
 };
 
 class Point
 {
      X x;
      Y y;
 public:
      Point(X inX, Y inY) : x(inX), y(inY) { }
      Point() { }
      void operator = (X inX) { x = inX; }
      void operator = (Y inY) { y = inY; }
      operator X () const { return x; }
      operator Y () const { return y; }
 };
 
 ostream& operator << (ostream& output, Point const& point)
 {
      output << X(point) << "," << Y(point);
      return output;
 }
 
 int main()
 {
      Point point;
      X x;
      Y y;
      x = X(17);
      cout << "point: " << point << "\nx    : " << x << "\ny    : " << y 
 << endl;
      point = x;
      point = Y(33);
      y = point;
      cout << "point: " << point << "\nx    : " << x << "\ny    : " << y 
 << endl;
 }


I'm not really a C++ coder so I had to make a few guesses as to what you
expected as the output. Anyhow, here is an attempt to code this in D ...

//--------------------------
import std.stdio;

class X
{
    private{
     int m;
    }
    // Constructors
    this(int in_val) { m = in_val;}
    this() { m = 0; }

    // Convert this object into a string form.
    char[] toString() { return std.string.format("%d", m); }
}

class Y
{
    private{
     int m;
    }
    // Constructors
    this(int in_val) { m = in_val;}
    this() { m = 0; }

    // Convert this object into a string form.
    char[] toString() { return std.string.format("%d", m); }
}

class Point
{
    private{
     X _x;
     Y _y;
    }
    // Constructors
    this(X inX, Y inY){ _x = inX; _y = inY; }
    this() { _x = new X; _y = new Y;}

    // Define some properties...
    void x(X inX) { _x = inX; }  // setter
    X x() { return _x; }         // getter

    void y(Y inY) { _y = inY; }  // setter
    Y y() { return _y; }         // getter

    // Convert this object into a string form.
    char[] toString() { return _x.toString ~ "," ~ _y.toString; }
}


int main()
{
     Point point = new Point;
     X x = new X;
     Y y = new Y;
     x = new X(17);
     writefln("point: " , point.toString, "\nx    : " , x.toString , 
              "\ny    : " , y.toString);
     point.x = x;
     point.y = new Y(33);
     y = point.y;
     writefln("point: " , point.toString, "\nx    : " , x.toString ,
              "\ny    : " , y.toString);
     return 0;
}
//--------------------------

This program produces the output ...

point: 0,0
x    : 17
y    : 0
point: 17,33
x    : 17
y    : 33

--------------------

The main differences are that you need to explicitly do a 'new' for objects
otherwise they are not created. There is no way to override the '='
operator in D, but there are 'properties' which replace a lot of uses for
'=' overriding. And 'ostream' stuff is generally handled by the toString
member function, though theoretically you could override the '<<' operator
but that is not the D way.

-- 
Derek
(skype: derek.j.parnell)
Melbourne, Australia
22/08/2005 10:01:47 AM

Aug 21 2005