I don't know rust, so pardon my lack of knowledge. But given a quick look, can't "traits" be seen just like "typeclasses" in haskell?
Btw, I feel like I should learn rust now.
Btw, I feel like I should learn rust now.
1. Rust's traits are unary relations (i.e., predicates) on types, whereas Haskell's type classes support relations of arbitrary arity ("multi-parameter type classes").
2. Rust's traits do not support higher kinds, so you can't define many things which are considered pretty basic to Haskell programmers (Functor, Monad, etc.).
But despite these limitations, Rust's traits are still great and better than what 99% of other languages have.
If you've got a Cat named puss, the call puss.meow() is effectively shorthand for something like Cat::meow(&puss) where that first parameter was the &self parameter to your "method".
Because this is namespaced, there's no problem if your Cat type has this meow() method and a Trait (say, AnimalNoises) it implements also has a meow() function, Rust knows those are different functions and the confusion only arises for a human reader, and only in code that actually wants to call one of the two identically named functions.
AnimalNoises::meow(&puss) and Cat::meow(&puss) are distinct, but writing thing.meow() requires inspecting other nearby code to discover whether from context this code knows thing is a Cat or just wants to make AnimalNoises. Where this might be confusing you should write AnimalNoises::meow(&thing) to make your intention clear to humans, and have it checked by the compiler.
Only the type's author gets to implement it, and only once (the standard library and especially core are special) so there's an essential distinction between SomeType::function() which was necessarily provided by the SomeType author, and just third party code that works with this type.
[Edited, this used to suggest it's a typo, but probably it's just a different way to think about what's happening, so I removed this claim]. There almost certainly isn't a Cat::clone and in fact what's happening is that Clone is in the prelude, so this is:
Clone::clone(&puss)
[edited to add]
Which is really even:
<Cat as Clone>::clone(&puss)
and because Rc is a Smart Pointer it implements DeRef and so that's ultimately:
<Cat as Clone>::clone(<Rc as Deref>::deref(&puss))
Definitely understandable that people want to write puss.clone() instead.
By the way, misfortunate::Multiplicity demonstrates Deref and DerefMut nicely, providing a type which has two things inside it but references to it act like one thing when being mutated and like the other when merely referenced...
Not something for absolute beginners, but worth seeing to build correct intuitions (and to underscore Rust's admonition not to implement Deref and DerefMut if you aren't a smart pointer -- misfortunate is like Jackass, this is for entertainment and not to be attempted in your real Rust projects).
But it’s true that much of the inspiration for Rust comes from functional languages, and the trait system is definitely inspired by Haskell.