Member delegate/fp to another member in same object?

[Juanjo Alvarez via Digitalmars-d-learn]

Hi!

I would like to have a "proxy" delegate, let's call it "foo" that 
could point to a method or another, let's call them "fast_foo" or 
"slow_foo" on the same object. This way depending on some 
conditions I could switch at runtime from one set of methods to 
others with a "switchFoo(" fast") method while the rest of the 
code inside the object would continue happily calling "foo".

The problem I have is that since the delegate keep the state of 
the object at the moment of the assignment I can't use it for 
this is pretty since the "fast/slow" methods need the value of 
the members of the enclosing object members at the point of 
usage,  I guess that I could pass the "this" pointer in the 
rebinding method but since the targets are also methods of the 
same object I wouldn't be surprised to find that there is an 
obvious/elegant  way to get access to "this" on the 
delegate-pointed method implementing.

Example:

struct S {
  int someState;
  void some_foo() { return this. someState;}

  void delegate() foo;

  void enable() {
    foo = &some_foo;
  }
}

unittest {
  S s;
  s.someState = 1;
  enable();
  s.someState = 2;
  assert(foo == 2);
  // fails because the delegate keeps
  // the state of the object at the
  // assignment point
}