Question

This doesn’t work in D:

void doSomething(auto a, auto b){
    // ...
}

I’m just curious, will this ever work? Or is this just technically impossible? (Or just plain stupid?)

In anyway, can this be accomplished in any other way? I suppose I could use the ... and look through the argument list, but I’m kinda making a library for lazy newbie people and want them to be able to create functions easily without really caring about data types. I’m playing with the idea of creating a struct called var like

struct var{
   byte type;
   void* data
   // ...
}

// and overload like all operators so that a lazy devver can do

var doSomething(var a, var b){
   if(a == "hello")
       b = 8;
   var c = "No.:" ~ b ~ " says:" ~ a; 
   return c;
}

But my head is already starting to hurt right there. And, I’m kinda feeling I’m missing something. I’m also painfully aware that this is probably what templates are for… Are they? From the little I know, a template would look like this (?)

void doSomething(T, U)( T a, U b){
   // ...
}

But now it doesn’t look so clean anymore. Maybe I’m getting all this backwards. Maybe my confusion stems from my belief that auto is a dynamic type, comparable to var i javascript, but when in reality, it’s something else?

And if it isn’t a dynamic type, and this is probably a whole other topic, is it possible to create one? Or is there maybe even an open source lib available? A liblazy maybe?

(PS. Yeah, maybe the lazy devver is me : )

Answer 1

I’ll just add that something close to your idea of runtime type polymorphism (the var structure) is already implemented in the std.variant module (D2 only).

Also, technically auto is really a keyword that does nothing – it’s used where you need a type modifier without a type. If you don’t specify a type, D will infer it for you from the initialization expression. For example, all of these work:

auto i = 5;
const j = 5;
static k = 5;