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

[Timon Gehr]

On 08/24/2011 07:54 PM, Steven Schveighoffer wrote:
On Wed, 24 Aug 2011 13:40:38 -0400, Andrej Mitrovic
<andrej.mitrov...@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..$]);
}