A Case For OOP?

Python’s standard library includes a very handy defaultdict. It behaves almost exactly like the standard dictionary except it’ll supply a pre-defined value for any non-existence keys. It is, unsurpringly, a subclass of dict.

I find my self missing this handy container in Swift. Especially when I use a normal Dictionary to accumulate/coalesce values under distinct keys. So I wrote my own:

There are a few noticable things about this implementation:

• It does not conform to the DictionaryLiteralConvertible protocol, for no good reasons, really. The initializer in this protocol takes a varadic argument. There’s no conevient way to forward this array to a normal dictionary’s initializer (incidentally, this is a Swift feature I really want). Plus, I don’t need DefaultDictionary to be a literal convertible.
• Most of the code, including the imaginary init mentioned in previous point, simply reuses stuff from Dictionary: asscociated type, indexes, generator, subscript, etc.

In comparison, Python implements defaultdict in a more intuitive way – via inheritance.

But do we want inheritance for structs and enums in Swift? What does that even mean? Is it simply a case that will go away when protocols become more powerful?