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What does assign a generic in a trait?
(lemmy.world)
Maybe the question is not well written, but it's because I do not really know what's happening in here. I'm learning Rust, I'm doing pretty good, but this is the second time that stomp with this.
First, I thought that only the Add trait would be enough, but the LSP keep saying me this if I do not add the "restriction", as far as I know.
What I do not get is what <Output = T> is. I know that is using the type T, but why it is assigned to Output?
The first time that I saw something similar was in the Rust book that comes with rustup, just look at the next function signature
Thank you for you help, you are awesome.
@capuccino You're not assigning anything. The Output = T is expressing a constraint. It's saying that the addition of T has to result in T again. A type can implement Add with any output type it wants.
I see. How can I define my own constraints in traits? Maybe seeing how to, I can full understand what's happening behind
@capuccino
A trait can have an associated type. You write this "trait Foo { type Bar; }". Then, when you implement the trait, you have to specify this type, with "type Bar = Something;". This is different from the trait itself being generic, because there can only be a single associated type, so you can't implement the trait multiple times with different associated types.
@capuccino
Then, when you write somewhere that some type satisfies a trait, like "T: Foo", and Foo has an associated type, you can further specify that not only does T need to implement Foo, but that the associated type satisfies some criteria.
You can do this two ways:
"Foo<Bar = Something>" says it has to be something specific,
"Foo<Bar: Baz>" says that it has to implement another trait
Amazing, so I can keep still using traits as constraints rather than types. I understand know. Hehehe, this is something that has been in my head since days ago