Naming convention for methods that modify vs methods that return new

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Is there some naming convention that's used to identify whether a method is going to perform an in-place modification [edit: I guess by this I really just mean a mutation] as opposed to returning a new instance of the same type?

Obviously you can look at the type signature to get this information but I've seen other languages (such as Swift if I recall correctly) that have such a convention, and am wondering if Rust has any similar conventions.

Thanks!

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I believe the convention is:

  • .set_foo(&mut self, Foo) for in-place mutation
  • .with_foo(self, Foo) -> Self for returning a new Self
  • .foo(&self, Foo) -> SelfBuilder when using the builder pattern

That is mostly for setting fields or individual attributes, in general there's no convention for methods taking &mut self vs self.

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I'm thinking no. For example, replace and replace_range: the former returns a new String and the latter modifies in-place. Looks like in Swift replace would be replaced, replacing, or replacement.

There isn't really anything going against Swift's convention, but I haven't seen any rules about this in particular.

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Thanks very much both!

@drewtato Yeah this seems to fit in with a few other examples I've seen in the standard library (and agreed re: Swift - and I very much like their approach here). I'll just have to be careful with my naming I think so that it tries to convey intent to calling code. Thank you!

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I don't apply this entirely consistently, but when I need the distinction I tend to lean toward: future-tense verb ⇒ operating on value in-place, past-tense verb ⇒ return new value. e.g. mutate ⇒ in-place, mutated ⇒ new value.

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Yeah I think this is what Swift does (it's been a while since I've worked with it), and it makes good sense to me. I'll probably adopt the same convention I think.

I have a feeling Ruby has a convention too, where mutating methods have a bang. This would obviously conflict with Rust's macro naming, but it's another example of what other languages do. Ah well!

Thanks!

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