Understanding isInfinite(Range)

[Steven Schveighoffer]

On Fri, 03 Sep 2010 11:12:29 -0400, Andrej Mitrovic  
<andrej.mitrovich at test.com> wrote:

> I was reading about the various range templates in std.range and I found  
> this:
>
> http://www.digitalmars.com/d/2.0/phobos/std_range.html#isInfinite
>
> Seems simple enough. But I dont understand it's implementation, this  
> from range.d:
>
> template isInfinite(Range)
> {
>     static if (isInputRange!Range && is(char[1 + Range.empty]))
>         enum bool isInfinite = !Range.empty;
>     else
>         enum bool isInfinite = false;
> }
>
> What does char[1 + Range.empty] do? It looks rather cryptic..

char[1+Range.empty] is a type.  If Range.empty is a compile-time constant,  
then this type is valid, otherwise it's not valid (the is expression  
results to true if the argument is a valid type).

If it's valid, then Range.empty never changes.  If it never changes and  
it's always false, then it's infinite.

-Steve