Static Length Propagation of Ranges

[Nordlöw via Digitalmars-d-learn]

On Wednesday, 19 October 2016 at 19:39:46 UTC, Nordlöw wrote:
> On Wednesday, 19 October 2016 at 19:01:50 UTC, Meta wrote:
>> https://goo.gl/t9m3YK
>>
>> I'm actually pretty impressed that this kind of code can be 
>> written in D.
>
> Thanks! Add at
>
> https://github.com/nordlow/phobos-next/blob/master/src/algorithm_ex.d#L2234

Made it even modular by factoring out arrayN at

https://github.com/nordlow/phobos-next/blob/master/src/algorithm_ex.d#L2200

and used at

https://github.com/nordlow/phobos-next/blob/master/src/algorithm_ex.d#L2215

Code:


ElementType!R[n] arrayN(size_t n, R)(R r)
{
     assert(r.length == n);
     typeof(return) dst;
     import std.algorithm.mutation : copy;
     r.copy(dst[]);
     return dst;
}

typeof(fun(E.init))[n] map(alias fun, E, size_t n)(const E[n] src)
{
     import std.algorithm.iteration : map;
     return src[].map!fun.arrayN!n;
}

@safe pure nothrow unittest
{
     import std.meta : AliasSeq;
     foreach (E; AliasSeq!(int, double))
     {
         enum n = 42;
         E[n] c;
         const result = map!(_ => _^^2)(c);
         static assert(c.length == result.length);
         static assert(is(typeof(result) == const(E)[n]));
     }
}