src/doc/reference/src/attributes/derive.md

   1 # Derive
   2
   3 The *`derive` attribute* allows new [items] to be automatically generated for
   4 data structures. It uses the [_MetaListPaths_] syntax to specify a list of
   5 traits to implement or paths to [derive macros] to process.
   6
   7 For example, the following will create an [`impl` item] for the
   8 [`PartialEq`] and [`Clone`] traits for `Foo`, and the type parameter `T` will be
   9 given the `PartialEq` or `Clone` constraints for the appropriate `impl`:
  10
  11 ```rust
  12 #[derive(PartialEq, Clone)]
  13 struct Foo<T> {
  14     a: i32,
  15     b: T,
  16 }
  17 ```
  18
  19 The generated `impl` for `PartialEq` is equivalent to
  20
  21 ```rust
  22 # struct Foo<T> { a: i32, b: T }
  23 impl<T: PartialEq> PartialEq for Foo<T> {
  24     fn eq(&self, other: &Foo<T>) -> bool {
  25         self.a == other.a && self.b == other.b
  26     }
  27 }
  28 ```
  29
  30 You can implement `derive` for your own traits through [procedural macros].
  31
  32 ## The `automatically_derived` attribute
  33
  34 The *`automatically_derived` attribute* is automatically added to
  35 [implementations] created by the `derive` attribute for built-in traits. It
  36 has no direct effect, but it may be used by tools and diagnostic lints to
  37 detect these automatically generated implementations.
  38
  39 [_MetaListPaths_]: ../attributes.md#meta-item-attribute-syntax
  40 [`Clone`]: ../../std/clone/trait.Clone.html
  41 [`PartialEq`]: ../../std/cmp/trait.PartialEq.html
  42 [`impl` item]: ../items/implementations.md
  43 [items]: ../items.md
  44 [derive macros]: ../procedural-macros.md#derive-macros
  45 [implementations]: ../items/implementations.md
  46 [items]: ../items.md
  47 [procedural macros]: ../procedural-macros.md#derive-macros