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_variables)] #fn main() { #[derive(PartialEq, Clone)] struct Foo<T> { a: i32, b: T, } #}
The generated impl
for PartialEq
is equivalent to
# #![allow(unused_variables)] #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 } fn ne(&self, other: &Foo<T>) -> bool { self.a != other.a || self.b != other.b } } #}
You can implement derive
for your own traits through procedural macros.