Derive
The derive
attribute allows new items to be automatically generated for
data structures. It uses the MetaListPaths syntax to specify a list of
traits to implement or paths to derive macros to process.
For example, the following will create an impl
item for the
PartialEq
and Clone
traits for Foo
, and the type parameter T
will be
given the PartialEq
or Clone
constraints for the appropriate impl
:
#![allow(unused)] fn main() { #[derive(PartialEq, Clone)] struct Foo<T> { a: i32, b: T, } }
The generated impl
for PartialEq
is equivalent to
#![allow(unused)] fn main() { struct Foo<T> { a: i32, b: T } impl<T: PartialEq> PartialEq for Foo<T> { fn eq(&self, other: &Foo<T>) -> bool { self.a == other.a && self.b == other.b } } }
You can implement derive
for your own traits through procedural macros.
The automatically_derived
attribute
The automatically_derived
attribute is automatically added to
implementations created by the derive
attribute for built-in traits. It
has no direct effect, but it may be used by tools and diagnostic lints to
detect these automatically generated implementations.