Meta-programming - examples

[kris]

janderson wrote:
> A couple of people have been asking questions about pseudo-real-life 
> examples for the new compile time code aspects of D.  I ask this 
> question for my interest as well.
> 
> Assuming that we have a good mechanism to process the input how could 
> compile time code improve your every-day proficiency?  (This is 
> specifically about the Mixin Expressions aspect).
> 
> I'll start with a few of my own.  Note my background is
> game-programming.  In my experience, we care constantly creating tools 
> to generate code because its impracticable to write and maintain it by 
> hand.
> 
> Statemachine (and AI logic) written by design and coders are common in 
> game programming.  Normally we have to fallback on a script language 
> which is never as powerful.
> 
> mixin(statemachine(
> "
>     state FireAtEnemy
>     {
>         transition EnemyRange < 10
>         {
>             goto ChaseEnemy
>         }
>         transition FacingEnemy < .2
>         {
>             goto ChaseEnemy
>         }
>     }
> 
>     state ChaseEnemy
>     {
>         ...
>     }
> 
> ");
> 
> You might imagine doing the above with if statement and arrays of 
> delegates however designers have a much harder time with that.
> 
> 3D Object rendering
> 
> //Render a 3D model.  For instance this may generate the vertexbuffers 
> and textures directly into code, or may extract some of the data from 
> the 3Dmodel.obj and load the rest at run-time.
> mixin(renderModel(import("3Dmodel.obj")));
> 
> Transforming Textures
> DXDtexture* texture = mixin(textureToD3D(import("3Dmodel.bmp")));
> 
> Simplify saving/loading of arbitrary structures.
> 
> //Only write this once.  Things are re-ordered for best fit in memory, 
> localization ect...
> mixin(Serailzable("Ship",
> "
>     struct Part
>     {
>         float firePower;
>         char[] Model;
>     }
> 
>     struct Ship
>     {
>         bool Friendly;
>         Part Parts[];
>     }
> ");
> 
> ... Later
> 
> Load("Ship", "Ship.asset");
> 
> GUI -> not sure about this one as I can't come up with a format thats 
> much neater then straight code. I'll post it anyways.
> 
> mixin(MyGUI(
> "
>     Button "OK", 10, 30
>     {
>         Exit;
>     }
> ");
> 
> Multi-threading
> 
> The suggestion with multi-threading I came up with a little while ago:
> 
> int[] array ...
> int result = 0;
> mixin(threadIt(
> "
>     foreach(A a; array)
>     {
>         result += a;
>     }
>     combiner //If necessary?
>     {
>         result = result[0] + result[1];
>     }
> ");
> 
> Compile time checking of code for coding standards or what have u:
> 
> mixin(CheckCode("
> 
> ect...
> 
> 
> ");
> //Note that there should be a way to disable CheckCode in the general 
> case to save compile time
> 
> 
> There's heaps of other stuff, but that would make this post way to long.
> 
> Personally I see this new mixin format as giving us the power to extend 
> D in whatever way meets our goals.  As Walter adds more features some of 
> them will be rarely used (law of demising returns) because they are 
> special case.  Mixin Expressions circumvent this because now the 
> programmer has the power to create the language features they need.
> 
> The only downside I see is compile-time, which I hope can be solved with 
> a smart caching system.


Thanks, very much. It's refreshing to see some concrete examples.

- Kris