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

[Jonathan M Davis]

On Wednesday, August 24, 2011 11:00 Timon Gehr wrote:
> On 08/24/2011 07:54 PM, Steven Schveighoffer wrote:
> > On Wed, 24 Aug 2011 13:40:38 -0400, Andrej Mitrovic
> > 
> > <andrej.mitrovich at gmail.com> 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) .. $]);
> >> process(1);
> >> }
> >> 
> >> void process(int[] vals...)
> >> {
> >> foreach (val; vals)
> >> {
> >> }
> >> }
> >> 
> >> Very simple, pass one or multiple arguments. But then I thought about
> >> using the `until` template instead of countUntil. However `until`
> >> returns a range. So my next guess was to write:
> >> 
> >> void main()
> >> {
> >> int[] a = [ 1, 2, 4, 7, 7, 2, 4, 7, 3, 5];
> >> 
> >> process(a.until(7)); // ok
> >> process(4); // error since 4 is not a range
> >> }
> >> 
> >> void process(Range)(Range vals) if (isInputRange!Range &&
> >> is(ElementType!Range == int))
> >> {
> >> foreach (val; vals)
> >> {
> >> }
> >> }
> >> 
> >> Is it somehow possible to automatically convert a literal to a range?
> >> I really miss the convenience of variadic functions. I thought about
> >> making an overload that only takes an int and constructing a simple
> >> input range around it so it can be passed to process(), e.g.:
> >> 
> >> void process(Range)(Range vals) if (isInputRange!Range &&
> >> is(ElementType!Range == int))
> >> {
> >> foreach (val; vals)
> >> {
> >> }
> >> }
> >> 
> >> void process(int arg)
> >> {
> >> process(makeInputRange(arg)); // make an input range, pass to
> >> above process()
> >> }
> >> 
> >> But I can't overload templated and non-templated functions, I think
> >> this is one of those old-standing bugs.
> > 
> > maybe:
> > 
> > void process(Range)(Range vals) if (isInputRange!Range &&
> > is(ElementType!Range == int))
> > {
> > ...
> > }
> > 
> > void process(Vals...)(Vals vals) if (allValsElementsAreInt)
> > {
> > ...
> > }
> > 
> > Note that I'm not sure what to put for allValsElementsAreInt...
> > 
> > -Steve
> 
> This should do (although it would probably be even better to have a
> forAll template and a predicate template).
> 
> template allElementsAreInt(T...){
> static if(T.length==0) enum allElementsAreInt=true;
> else enum allElementsAreInt=is(typeof(T[0])==int)
> && allElementsAreInt!(T[1..$]);
> }

std.typetuple has anySatisfy and allSatisfy (though that's a rather bizarre 
place to put them IMHO).

- Jonathan M Davis