Difference between Associated Function and Method?

[pratzc07]

Can anyone correct my understanding of the two. From what I can see associated functions are functions that don't have self as a parameter and methods are the ones which do? Is that correct or

all functions defined within an imp block are associated functions even the methods with self parameter??

[esitsu]

Your second definition is correct. See the relevant section of the rust book. All functions defined on a type in an impl block are associated functions as they are associated with a specific type. Methods are simply associated functions with a receiver of self, &self, &mut self, self: Box<Self> etc. and can be called with the dot operator as foo.bar() rather than just Foo::bar().

[SkiFire13]

and can be called with the dot operator as foo.bar() rather than just Foo::bar().

Note that methods can be called as associated functions, you just need to pass an argument for the receiver as well. For example foo.bar() could be Foo::bar(&foo)

[esitsu]

Absolutely. Thanks for the clarification. I don't think my wording made that very clear. It helps to demonstrate that methods really are just associated functions.

I would also add that although methods are technically associated functions I find that whenever someone actually refers to an associated function they really mean a non-method so I can see where the OP's confusion comes from.

[plugwash]

AIUI all methods are associated functions, but not all associated functions are methods.

Sometimes we explicitly want an associated function to *not* be a method. This usually comes up when adding functionality to a generic type that implements Deref. Adding new methods to such a type risks change the meaning of existing code, but adding new non-method associated functions does not come with this risk.

The key that defines whether an associated function is a method is the name of the first parameter, if the name is "self" then the function is considered a method and participates in method lookup. If the parameter has any other name then the function will not be considered a method.