What should coercion look like for R7?

[hadley]

No description provided.

[lawremi]

How about it behaves like methods::as() but with a verb like cast()? Ideally cast() would itself be a generic, with special behavior, so we can avoid the as()/coerce() duality.

Note that this would be distinct from up casting for affecting dispatch, such as when calling the next method, because casting to affect dispatch should only modify the class, not the structure (so that any extra fields are carried along), and the class modification must be transient so that any dispatch in the next method behaves correctly.

[hadley]

I think the challenge of avoiding two functions is that you want to write cast(object, class) but dispatch on class, object_class(object)).

[hadley]

(Note to self: remember to also incorporate r7_data() into this)

[lawremi]

Agreed that the dispatch behavior is weird, but we can implement cast() as a non-standard generic to achieve that.

[hadley]

Very initial thoughts:

cast <- R7_generic("cast", c("from", "to"), function(from, to, ...) {
  signature <- list(to = object_class(to), from = from)
  cast <- method(cast, signature)
  cast(object, ...)
})