A refinement for pure implementation

[bearophile]

Do you remember if Hara has implemented a patch to allow a2 to be 
immutable?

int[] foo1(int x) pure {
    return null;
}
int[] foo2(string s) pure {
    return null;
}
void main() {
    immutable a1 = foo1(10); // OK
    immutable a2 = foo2("hello"); // currently error
}


The idea behind this is that the type of s is different from the 
return type of foo2, so foo2 is a strongly pure function.

Bye,
bearophile