IMO Dart has the best implementation of properties, which you can start out as normal fields, e.g:

    class Rectangle {
      num left, top, width, height, right bottom;
    }

and can access like normal:

    var height = rect.bottom - rect.top;

But can later be changed into a computed property without affecting the above callsites, e.g:

    class Rectangle {
      num left, top, width, height;

      num get right             => left + width;
          set right(num value)  => left = value - width;
      num get bottom            => top + height;
          set bottom(num value) => top = value - height;
    }

C# is a close 2nd, but it's not binary (or reflection) compatible to change from a field to a property for call-sites (i.e. it's only source-compatible).