Rewriting a c++ template to D (replacing iterator with ranges "properly")

[aliak]

On Friday, 26 January 2018 at 14:59:09 UTC, Simen Kjærås wrote:
> what is N here? You're declaring it to be an int value in the 
> template<> definition, and then use it as a type in the 
> function definition.

Oops again :) Should've been typename N (where N is some integral 
type).

> Not exactly. range.front will assert after the last popFrontN 
> (since the range is empty).

Ya, sorry, realized this a bit after I posted.

> It's trying to combine 3 and 4 I think, but it fails because 
> this is allowed in D:
>
> int a;
> a = false;

Ah true, so it's more of a is(ElementType!R : bool) check?

>
> You'll want to pass the range as ref. hasLvalueElements checks 
> if the elements have lvalue semantics

Doh, of course. It's in the name even!

> import std.range;
>
> struct R {
>     int[3] elements;
>     int index;
>
>     ref auto front() {
>         return elements[index];
>     }
>
>     void popFront() {
>         ++index;
>     }
>
>     bool empty() {
>         return index >= elements.length;
>     }
> }
>
> unittest {
>     assert(hasLvalueElements!(R));
>     auto a = R([1,2,3], 0);
>     auto b = a;
>     b.front = 4;
>     assert(a.elements == [1,2,3]);
>     assert(b.elements == [4,2,3]);
> }
>
> As we can see, b is a complete copy of a, and changing b does 
> not change a. The exact same behavior would occur if a was 
> passed by value to a function.
>
> --
>   Simen

Thanks for the input!