2013/9/20 Andrei Alexandrescu <SeeWebsiteForEmail@erdani.org>

Consider a struct that may or may not have state depending on a type parameter:

struct S(T)
{
  enum hasState = FieldTypeTuple!T.length || isNested!T;
  static if (hasState)
    T _theT;
  else
    alias _theT = T;
  ...
}

This is really nice because I don't bloat S unnecessarily and I get to use _theT.method() uniformly whether or not it's the type itself or the data member.

The duplication problem appears when S itself must define a method that should be static or nonstatic depending on the existence of state. Consider:

struct S(T)
{
  ... continued from above ...
  if (hasState)
    int method() { return 1 + _theT.method(); }
  else
    static int method() { return 1 + _theT.method(); }
}

In the general case the body of S!T.method() may be of course larger, which makes for a nasty duplication - essentially all but the "static" keyword must be duplicated.

Any ideas for a clean solution? I can't get much further than string mixins, which wouldn't be clean :o).

Just an idea: string mixin + UDA?