Idea: extend typesafe variadic functions

[Daniel Keep]

Jarrett Billingsley wrote:
> One of the "cool features you probably didn't know about" with typesafe 
> variadic functions is that you can make a variadic class parameter which 
> will be constructed with the parameters to the function, like so:
> 
> class A
> {
>     this(int x, float y){}
> }
> 
> void func(A a...)
> {
> 
> }
> 
> ....
> 
> func(3, 4.5);
> 
> This will implicitly call the constructor for A when you call func() and 
> will forward those parameters to the class constructor.

*Boggle*  When did *that* happen?!

> What would be really cool is to have this happen for an array of classes or 
> structs as well:
> 
> class A
> {
>     this(int x) {}
>     this(float x) {}
>     this(char[] s) {}
> }
> 
> void func(A[] args...)
> {
> 
> }
> 
> ....
> 
> func(1, 2.3, "hi");
> 
> Right now, it says "cannot implicitly convert 1 to A" or something, but with 
> this new feature, this would construct three instances of A, one using the 
> int constructor, one using the float, and one using the string.  Of course, 
> for sanity's sake, it would only try to construct As using single-parameter 
> constructors.
> 
> This would work similarly for structs:
> 
> struct S
> {
>     static S opCall(T)(T value)
>     {
>         S s;
>         return s;
>     }
> }
> 
> void func(S[] args...)
> {
> 
> }
> 
> ....
> 
> func(1, 2.3, "hi");
> 
> (See if you can figure out why I think this would be cool.. ;) ) 

I'm afraid I can't :(

I imagine that there's probably some very nice things you could do with
this, but I can't see why you couldn't do it already:

void funcT(Ts...)(Ts args)
{
    A[] as;
    as.length = args.length;
    foreach( i, arg ; args )
        as[i] = new A(arg);

    func(as);
}

Getting this to work with overloads would be... interesting, but
certainly doable.  Heck, you could probably turn the above into a
generic templated "array-of-T" initializer.

On a side note, am I the only one who is *really* uncomfortable with the
fact that the first example works at all?  :S

	-- Daniel

-- 
int getRandomNumber()
{
    return 4; // chosen by fair dice roll.
              // guaranteed to be random.
}

http://xkcd.com/

v2sw5+8Yhw5ln4+5pr6OFPma8u6+7Lw4Tm6+7l6+7D
i28a2Xs3MSr2e4/6+7t4TNSMb6HTOp5en5g6RAHCP  http://hackerkey.com/