DIP1000: 'return scope' ambiguity and why you can't make opIndex work

[Walter Bright]

Added PRs:

https://github.com/dlang/dmd/pull/12817
https://github.com/dlang/dmd/pull/12819

This, of course, breaks:

  struct Vector {
     float[] _elements;
     ref float opIndex(size_t i) scope return {
         return this._elements[i];
     }
  }

as Dennis points out. It still is the correct fix, however, we just have to find 
a way to get opIndex to work.