How do I simulate variadic parameters for template (range) functions?

[Timon Gehr]

On 08/24/2011 07:40 PM, Andrej Mitrovic wrote:
> Here's what I can do with a variadic function:
>
> void main()
> {
>      int[] a = [ 1, 2, 4, 7, 7, 2, 4, 7, 3, 5];
>
>      process(a[a.countUntil(7) .. $]);
>      process(1);
> }
>
> void process(int[] vals...)
> {
>      foreach (val; vals)
>      {
>      }
> }
>
> Very simple, pass one or multiple arguments. But then I thought about
> using the `until` template instead of countUntil. However `until`
> returns a range. So my next guess was to write:
>
> void main()
> {
>      int[] a = [ 1, 2, 4, 7, 7, 2, 4, 7, 3, 5];
>
>      process(a.until(7));  // ok
>      process(4);  // error since 4 is not a range
> }
>
> void process(Range)(Range vals) if (isInputRange!Range&&
> is(ElementType!Range == int))
> {
>      foreach (val; vals)
>      {
>      }
> }
>
> Is it somehow possible to automatically convert a literal to a range?
> I really miss the convenience of variadic functions. I thought about
> making an overload that only takes an int and constructing a simple
> input range around it so it can be passed to process(), e.g.:
>
> void process(Range)(Range vals) if (isInputRange!Range&&
> is(ElementType!Range == int))
> {
>      foreach (val; vals)
>      {
>      }
> }
>
> void process(int arg)
> {
>      process(makeInputRange(arg));  // make an input range, pass to
> above process()
> }
>
> But I can't overload templated and non-templated functions, I think
> this is one of those old-standing bugs.

Workaround: You can make it a templated function with no template 
arguments and wrap a non-templated version, if it is important that the 
implementation is not a template.