Template specialization

[Marc Schütz via Digitalmars-d-learn]

On Friday, 22 January 2016 at 01:33:42 UTC, Darrell Gallion wrote:
> void foo(A)()
>         if (!is (A == int)) {
>     pragma(msg, "int");
> }
>
> void foo(A)()
>         if (is (A == int[])) {
>     pragma(msg, "int[]");
> }
>
> void main() {
>
>   foo!(int)();
>   foo!(int[])();
> }
>
> ===========
>
> source\app.d(15): Error: template app.foo cannot deduce 
> function from argument types !(int)(), candidates are:
> source\app.d(3):        app.foo(A)() if (!is(A == int))
> source\app.d(8):        app.foo(A)() if (is(A == int[]))
> source\app.d(16): Error: app.foo called with argument types () 
> matches both:
> source\app.d(3):     app.foo!(int[]).foo()
> and:
> source\app.d(8):     app.foo!(int[]).foo()

Have a look at the first template constraint. It checks whether 
the template parameter _is not_ `int`, so of course, the first 
instantiation fails, and the second one is ambiguous.