No shortcircuit for static if or template constraints?

[stewart via Digitalmars-d-learn]

Hi All,

Given this code:
---
import std.traits;
import std.range;
import std.stdio;

enum isSupportedRange(T) = (isInputRange!T && 
isIntegral!(ForeachType!T));

void func(T)(T vals)
{
    static if(isSupportedRange!T) {
        // Do something with a range
    } else {
        // Do something with a scalar
    }
}

void main() {
    int a1 = 0;
    int[] a2 = [1,2,3];

    func(a1);
    func(a2);
}
---

I a compile error like so:

...std/traits.d(6136): Error: invalid foreach aggregate 0
hack.d(6): Error: template instance std.traits.ForeachType!int 
error instantiating
hack.d(10):        instantiated from here: isSupportedRange!int
hack.d(22):        instantiated from here: func!int

However, if I remove the Foreach part the "isInputRange!T" 
clearly fails.

I also tried overloading the function like so:

---
enum isSupportedRange(T) = (isInputRange!T && 
isIntegral!(ForeachType!T));

void func(T)(T vals) if(isSupportedRange!T) {
        // Do something with a range
}
void func(T)(T vals) if(isNumeric!T) {
    // Do something with a scalar
}
---

Again, if I remove the Foreach part and ignore element type of 
the range it works OK.

Am I doing something wrong?

Thanks,
stew