Automatic range creation for class or struct?

[cym13 via Digitalmars-d-learn]

On Wednesday, 10 February 2016 at 00:05:36 UTC, Peka wrote:
> Hi!
>
> I have class (or struct) which realises .length() and 
> .opIndex(size_t) methods.
>
> It is possible to create from this class some sort of range 
> using template from std? (I mean that internal counter, 
> .popFront(), .empty() etc methods should be added by template.)

I don't think anything like that exists in phobos but it's not 
hard to pull it out using mixin templates:


mixin template Rangify(T)
if (__traits(hasMember, T, "length")
  && __traits(hasMember, T, "opIndex")) {

     ulong _counter;

     bool empty() {
         return _counter == this.length;
     }

     auto front() {
         return this[_counter];
     }

     auto popFront() {
         _counter++;
     }
}

struct S {
     int[] arr;

     mixin Rangify!S;

     auto length() {
         return arr.length;
     }

     int opIndex(size_t i) {
         return arr[i];
     }
}

void main(string[] args) {
     import std.stdio: writeln;

     auto s = S();
     s.arr = [1, 2, 3];

     foreach (x ; s)
         writeln(x);
}