Re: "fold": a replacement for "reduce"

[monarch_dodra]

On Monday, 31 March 2014 at 10:28:10 UTC, bearophile wrote:
monarch_dodra:
Thank you for the answers.

I can get it to work for fold though.

Good.

I've reconsidered my answer. It is *impossible* to get what you 
are asking for to work, without explicitly passing a seed.

This is because the seed is *initialized* to the range's front. 
Anything other than "const(uint)[]" would simply break the type 
system: If your range only has 1 element, then you'd be returning 
a mutable reference to const data.

So my vote goes to this solution.

//----
uint[] foo3(in uint[][] X)
{
    assert(!X.empty)
    auto seed = X.front.dup;
    X.popFront();
    return reduce!((i, j) => zip(i, j)
                             .map!(kw => kw[0] | kw[1])
                             .array)
                  (seed, X);
}
//----

I re-wrote it that way: It's a bit longer, but a bit more generic 
in terms of customizing your seed.