Struct "inheritance"

[Ali Çehreli]

On 02/04/2012 03:38 AM, Vidar Wahlberg wrote:

 > Let's say I got a struct for a location on a 2-dimensional plane:
 > struct Point {
 > int x;
 > int y;
 > }
 > Further I also need to represent a location in a 3-dimensional space:
 > struct Coordinate {
 > int x;
 > int y;
 > int z;
 > }
 > If these were classes instead I could simply make Coordinate inherit
 > from Point and only add "int z;".

There is also template mixins to inject complete features into the code 
(similar to C macros but without their gotchas).

The following templatizes the coordinate types, but you could use put 
write everywhere:

import std.stdio;

template Point2D(T)
{
     T x;
     T y;

     void foo2D()
     {
         writefln("Using (%s,%s)", x, y);
     }
}

struct Coordinate(T)
{
     mixin Point2D!T;   // <-- Inject x, y, and foo2D() here
     T z;

     this(T x, T y, T z)
     {
         this.x = x;
         this.y = y;
         this.z = z;
     }
}

void main()
{
     auto c = Coordinate!double(1.1, 2.2, 3.3);
     c.foo2D();
}

You could insert the following line in any other scope and you would 
have x, y, foo2D() inserted right there as well:

     if (someCondition) {
         mixin Point2D!T;   // <-- Inject x, y, and foo2D() here

         // ... use the local x, y, and foo2D() here
     }

Of course 'static if' may be even more suitable in other cases.

Ali