[hackathon] An article about metaprogramming

[bearophile via Digitalmars-d]

Mafi:

> https://marfisc.wordpress.com/2015/04/29/using-d-templates-for-gamedev/
>
> What do you think? Any remarks?

>The SDL_Event is a union. Accessing it is inherently unsafe for 
>type consistency and memory safety. The SDL library mitigates 
>this problem by adding a tag (the member type) which encodes 
>which union-member is to be used.<

In Rust you use the built-in tagged unions and call it a day...



switch(polledEvent.type) {
     mixin(caseOnEvent!("SDL_QUIT", "quit"));
     mixin(caseOnEvent!("SDL_ACTIVEEVEENT", "active"));
     mixin(caseOnEvent!("SDL_KEYDOWN", "eventKeyDown")); // (*)
     mixin(caseOnEvent!("SDL_KEYUP", "eventKeyUp")); // (*)
     mixin(caseOnEvent!("SDL_MOUSEMOTION", "motion"));
     mixin(caseOnEvent!("SDL_MOUSEBUTTONUP", 
"eventMouseButtonUp")); // (*)
     mixin(caseOnEvent!("SDL_MOUSEBUTTONDOWN", 
"eventMouseButtonDown")); // (*)
     mixin(caseOnEvent!("SDL_JOYAXISMOTION", "jaxis"));
     mixin(caseOnEvent!("SDL_JOYBALLMOTION", "jball"));
     mixin(caseOnEvent!("SDL_JOYHATMOTION", "jhat"));
     mixin(caseOnEvent!("SDL_JOYBUTTONDOWN", 
"eventJoyButtonDown")); // (*)
     mixin(caseOnEvent!("SDL_JOYBUTTONUP", "eventJoyButtonUp")); 
// (*)
     mixin(caseOnEvent!("SDL_USEREVENT", "user"));
     mixin(caseOnEvent!("SDL_SYSWMEVENT", "syswm"));
default: //has to be there even if empty
     static if(is(typeof(that.onOther(Event.init)))) {
         that.onOther(polledEvent); break;
     }
}

The default should be aligned just like the other cases. Often is 
a good idea to use "final switch" with enumerations.
Probably there are ways to make that code more dry, using a 
TypeTuple of pairs like ("SDL_QUIT", "quit").

Bye,
bearophile