Const-correctness and uniqueness. Again.

[Tobias Pankrath via Digitalmars-d]

On Monday, 9 February 2015 at 12:39:06 UTC, Marc Schütz wrote:
> On Monday, 9 February 2015 at 11:38:23 UTC, Jakob Ovrum wrote:
>> On Monday, 9 February 2015 at 11:37:23 UTC, Jakob Ovrum wrote:
>>> std.array.join is strongly pure (with appropriate template 
>>> arguments), so its return value is implicitly convertible to 
>>> immutable.
>>
>> Err, implicitly convertible to *mutable*. It goes both ways.
>
> It does? Not according to my tests. And it would be bad if it 
> did, because the returned immutable value could actually reside 
> in read-only memory.

join returns a mutable array, that can be implicitly casted to 
immutable if join is pure.

BTW, that was hard to figure out, because

ElementEncodingType!(ElementType!RoR)[] join(RoR, R)(RoR ror, R 
sep) if (isInputRange!RoR && 
isInputRange!(Unqual!(ElementType!RoR)) && isInputRange!R && 
is(Unqual!(ElementType!(ElementType!RoR)) == 
Unqual!(ElementType!R)));
ElementEncodingType!(ElementType!RoR)[] join(RoR)(RoR ror) if 
(isInputRange!RoR && isInputRange!(Unqual!(ElementType!RoR)));

and ElementEncodingType is not linked.

That would read so much better as

let
    alias C = ElementEncodingType!(ElementType!RoR)
    alias ERT = Unqual!(ElementType!RoR)
    alias ET = ElementType!ERT
in
    C[] join(RoR, R)(RoR ror, R sep)
    if(  isInputRange!(RoR) && isInputRange!ERT && isInputRange!R
      && is(ET == ElementType!R))

    C[] join(RoR)(RoR ror)
      if( isInputRange!RoR) && isInputRange!ERT )


Do our planned ddo[c|x] enhancement make this possible?