Cartesian product of immutable ranges

[Stanislav Blinov]

On Sunday, 26 January 2014 at 21:49:37 UTC, matovitch wrote:

> void main() {
>
>     immutable int[] B = [ 1, 2, 3 ];
>     immutable int[] C = [ 4, 5, 6 ];
>     auto BC = zip(B, C);
>     writeln(BC);
> }
>
> Here B and C aren't inputRange thought acording to the template 
> constraint of zip there should be. How can it compiles ?

B and C aren't, but B[] and C[] are. That's what's going on when
you pass an array as function argument: a full slice is taken.
See for yourself:

void foo(R)(R r) {
      writeln(R.stringof);
}

foo(B); // will print immutable(int)[]

> How to compute the cartesian product of two immutable ranges ?

Short answer: with std.algorithm - you can't. Because internally
it (Zip, actually) performs assignments, and you can't assign to
immutable(T).

Why?