Functions and methods

Prefer methods to functions if there is a clear receiver. [FIXME: needs RFC]

Prefer

impl Foo {
    pub fn frob(&self, w: widget) { ... }
}

over

pub fn frob(foo: &Foo, w: widget) { ... }

for any operation that is clearly associated with a particular type.

Methods have numerous advantages over functions: * They do not need to be imported or qualified to be used: all you need is a value of the appropriate type. * Their invocation performs autoborrowing (including mutable borrows). * They make it easy to answer the question "what can I do with a value of type T" (especially when using rustdoc). * They provide self notation, which is more concise and often more clearly conveys ownership distinctions.

[FIXME] Revisit these guidelines with UFCS and conventions developing around it.

Guidelines for inherent methods. [FIXME]

[FIXME] We need guidelines for when to provide inherent methods on a type, versus methods through a trait or functions.

NOTE: Rules for method resolution around inherent methods are in flux, which may impact the guidelines.