Better idea for double list comprehension?

[bearophile]

CJS:

> I'm trying to write a D function that does the same as this 
> Python function:
>
> def cross(A, B):
>     "Cross product of elements in A and elements in B."
>     return [a+b for a in A for b in B]
>
> where A and B are strings. (So cross("ab","12") is ["a1", "b1", 
> "a2", "b2"]).

One solution:


import std.stdio, std.conv, std.algorithm, std.array;

string[] cross(in string A, in string B) {
     return cartesianProduct(A, B).map!(ab => ab[].text).array;
}

void main() {
     cross("ab", "12").writeln;
}


But note that currently cartesianProduct doesn't return the pairs 
in a natural order.

cross() should be pure.

Bye,
bearophile