# Using `#[derive(Deref)]` Deriving `Deref` only works for a single field of a struct. It's possible to use it in two ways: 1. Dereferencing to the field, i.e. like if your type was a reference type. 2. Doing a dereference on the field, for when the field itself is a reference type like `&` and `Box`. With `#[deref]` or `#[deref(ignore)]` it's possible to indicate the field that you want to derive `Deref` for. ## Example usage ```rust # use derive_more::Deref; # #[derive(Deref)] struct Num { num: i32, } #[derive(Deref)] #[deref(forward)] struct MyBoxedInt(Box<i32>); // You can specify the field you want to derive `Deref` for. #[derive(Deref)] struct CoolVec { cool: bool, #[deref] vec: Vec<i32>, } let num = Num{num: 123}; let boxed = MyBoxedInt(Box::new(123)); let cool_vec = CoolVec{cool: true, vec: vec![123]}; assert_eq!(123, *num); assert_eq!(123, *boxed); assert_eq!(vec![123], *cool_vec); ``` ## Structs When deriving a non-forwarded `Deref` for a struct: ```rust # use derive_more::Deref; # #[derive(Deref)] struct CoolVec { cool: bool, #[deref] vec: Vec<i32>, } ``` Code like this will be generated: ```rust # struct CoolVec { # cool: bool, # vec: Vec<i32>, # } impl derive_more::Deref for CoolVec { type Target = Vec<i32>; #[inline] fn deref(&self) -> &Self::Target { &self.vec } } ``` When deriving a forwarded `Deref` for a struct: ```rust # use derive_more::Deref; # #[derive(Deref)] #[deref(forward)] struct MyBoxedInt(Box<i32>); ``` Code like this will be generated: ```rust # struct MyBoxedInt(Box<i32>); impl derive_more::Deref for MyBoxedInt { type Target = <Box<i32> as derive_more::Deref>::Target; #[inline] fn deref(&self) -> &Self::Target { <Box<i32> as derive_more::Deref>::deref(&self.0) } } ``` ## Enums Deriving `Deref` is not supported for enums.