extend e language

The best way to do it, from an encapsulation point of view, is to declare a separate determinant field that has the same value for 'ONE' and 'TWO'. Let's use a simple boolean in this case:

extend foo_u {

  is_1_or_2 : bool;

  keep is_1_or_2 == foo_field in [ ONE, TWO ];

};

extend TRUE'is_1_or_2 foo_u {

  some_field : some_type_t;

  // enjoy here

};

This way, the extra code is truly common. Let's say that you define 'some_field' in both ways (with the macro and with the common determinant). This means, if you want to access 'some_field' in the macro case you have to cast to different types depending on the value of 'foo_field':

'foo.as_a(ONE foo_u).some_field' or 'foo.as_a(TWO foo_u).some_field'

In the other case, it's enough to say:

'foo.as_a(TRUE foo_u).some_field'

This cast will work for both 'ONE' and 'TWO' foos.

The second approach is much better if you need to write generic code that handles fields defined in the extensions you want to add. If you don't need this and you only want to define extensions to methods, then the macro approach also works.

Good idea.

Thanks,

Catalin