static data in a sub-class

[Ali Çehreli]

On 12/23/2012 02:08 PM, Steve D wrote:

 > Let's say it's a game and the objects are creatures.

Thanks for giving more context. It helps to see meaningful names to 
understand code better.

 > class Creature {
 > abstract void move();
 > }

That's very reasonable.

 > class Monster :Creature {
 > static float[3] hi = 1;
 >
 > this(float[] x=null) {if (x) hi = x;}

That is a bad idea. x is passed to a single Monster object but the 'hi' 
static member of the whole Monster class gets affected. Just because 
there is a SwiftMonster, all Monsters become swift.

This shows that it would be better to mark 'hi' as immutable to avoid 
such mistakes.

 > Why Ali? Why?
 > Why aren't things simple?

:) I still think making Monster a template is a better way to go:

import std.stdio;

class Creature {
     abstract void move();
}

class MonsterImpl(SubT) : Creature {
     final void run() {  writefln("hi running at %s", SubT.hi);  }

     override void move() { run(); }
}

class RegularMonster : MonsterImpl!RegularMonster {
     static immutable float[3] hi = 1;
}

class SwiftMonster : MonsterImpl!SwiftMonster {
     static immutable float[3] hi = 2;
}

void main()
{
     Creature[2] creatures;
     creatures[0] = new RegularMonster();
     creatures[1] = new SwiftMonster();
     foreach(c; creatures) c.move();
}

The output:

hi running at [1, 1, 1]
hi running at [2, 2, 2]

Ali