[minamea]

I urge you to take this criticism more seriously. With your library a programmer is changing the semantics of class nesting in the language, all by pre-pending a very missable and ambiguous @case to the class. I'm no expert but I think this is pretty bad in any language, and especially one that says "explicit is better than implicit"

[lihaoyi]

We do take it seriously; it's a hard tradeoff between Novelty and Utility. Given that the whole point of macros is to change the semantics of the Python language, this (valid) criticism applies not just to case classes but macros in general. If you go haywire with macros, all hell breaks loose.

We think that with some discipline, it is possible to come up with macro transformations which are both useful and understandable by a programmer. This means setting clearly defined semantics for the transformations, which is difficult but doable.

If you think macros are kinda crazy (well, they are!) you should look at the implementation of such pythonic constructs like `namedtuple`, the `ast` module and the new Enum library coming out!

[michaelhoffman]

The implementation of namedtuple is pretty crazy, but the interface is simple and doesn't change the language semantics.

[lihaoyi]

I'd argue that "fields as a string with spaces inside, or maybe a list of strings" is changing language semantics quite a bit.

We're used to namedtuples doing it like this now, but if namedtuples didn't exist, "fields as a list of strings with spaces inside, or maybe a list of strings" would definitely not make it past code review and probably get me yelled at by my future colleagues.

[jnhnum1]

Yes, it could be bad, but at the same time the "@case" isn't the only indicator that this class is special. A case class definition can be very visually distinct compared to a normal class.

One thing case classes let you do is implement functionality externally to a class using pattern-matching functions. When you do this, your case class definition will consist of nothing but empty class definitions:

  @case
  class List:
    class Nil():  pass
    class Cons(x, xs): pass

In any case, Python's enums will use fully qualified names, so we may change our current system for compatibility and consistency.