Static Length Propagation of Ranges

[Meta via Digitalmars-d-learn]

On Wednesday, 19 October 2016 at 18:56:35 UTC, Meta wrote:
> Couldn't you do this? Mind you I'm not able to test the code 
> right now, but I think it can work with some tweaking.
>
> typeof(fn(E.init))[n] map1(alias fn, E, size_t n)(E[n] 
> container)
> {
>     import std.algorithm.iteration : map;
>     import std.array : array;
>
>     typeof(return) sres;
>     return container[].map!fn.copy(sres[]);
> }
>
> @safe pure nothrow unittest
> {
>    int[42] c;
>    //result should be a static array of length 42
>    auto result = map1!(_ => _^2)(c);
> }

Sorry, that code had a few mistakes. The working code:

import std.algorithm;
import std.range;

typeof(fn(E.init))[n] map1(alias fn, E, size_t n)(E[n] container)
{
     import std.algorithm.iteration : map;
     import std.array : array;

     typeof(return) sres;
     container[].map!fn.copy(sres[]);
     return sres;
}

void main()
{
    int[42] c;
    //result should be a static array of length 42
    auto result = map1!(_ => _^2)(c);
    assert(is(typeof(result) == typeof(c)));
}

https://goo.gl/t9m3YK

I'm actually pretty impressed that this kind of code can be 
written in D.