Build all combinations of strings

["Nordlöw" via Digitalmars-d-learn]

On Monday, 11 June 2012 at 19:52:38 UTC, bearophile wrote:
> Using that the code is:
>
> import std.string, std.stdio, std.array;
> void main() {
>     auto words = "foo bar doo".split();
>     auto res = permutations!false(words).map!(p => p.join(" 
> "))().array();
>     writeln(res);
> }

Is doCopy really needed as an argument here?

Couldn't this be inferred from the mutability of T instead?