CODEWITHSUNDEEP
rust
VP.
VP.

Reputation: 16705

Why some rust types provide static methods instead of object methods?

Looking at the Rc interface I found that the Rc struct has methods but they are defined without self so they are static but nothing actually prevents them to be usual object methods. The question is why they are defined so? Why, for example, the Rc::weak_count is defined in the form:

fn weak_count(this: &Rc<T>) -> usize

instead of:

fn weak_count(&self) -> usize

Upvotes: 3

Views: 418

Answers (1)

Rufflewind
Rufflewind

Reputation: 8956

It is to prevent shadowing methods that would otherwise be visible through the Deref and DerefMut implementations of Rc. To quote the documentation of Rc:

The inherent methods of Rc are all associated functions, which means that you have to call them as e.g. Rc::get_mut(&mut value) instead of value.get_mut(). This avoids conflicts with methods of the inner type T.

For example, if you have Rc<Foo> where Foo defines its own method called weak_count, using a static method would allow the user to write foo.weak_count(…) to call Foo::weak_count and Rc::weak_count(&foo) to call Rc::weak_count.

(For this reason, adding an intrinsic method to a type that defines Deref / DerefMut will break backward compatibiltiy).

Upvotes: 9

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