Crate derive_more [−] [src]

derive_more

Rust has lots of builtin traits that are implemented for its basic types, such as Add, Not or From. However, when wrapping these types inside your own structs or enums you lose the implementations of these traits and are required to recreate them. This is especially annoying when your own structures are very simple, such as when using the commonly advised newtype pattern (e.g. MyInt(i32)).

This library tries to remove these annoyances and the corresponding boilerplate code. It does this by allowing you to derive lots of commonly used traits for both structs and enums.

Example code

By using this library the following code just works:


#[derive(Debug, Eq, PartialEq, From, Add)]
struct MyInt(i32);

#[derive(Debug, Eq, PartialEq, From, Into, Constructor, Mul)]
struct Point2D {
    x: i32,
    y: i32,
}

#[derive(Debug, Eq, PartialEq, From, Add)]
enum MyEnum {
    Int(i32),
    UnsignedInt(u32),
    Nothing,
}

fn main() {
    let my_11 = MyInt(5) + 6.into();
    assert_eq!(MyInt(11), MyInt(5) + 6.into());
    assert_eq!(Point2D { x: 5, y: 6 } * 10, (50, 60).into());
    assert_eq!((5, 6), Point2D { x: 5, y: 6 }.into());
    assert_eq!(Point2D { x: 5, y: 6 }, Point2D::new(5, 6));
    assert_eq!(MyEnum::Int(15), (MyEnum::Int(8) + 7.into()).unwrap())
}

The newly derivable traits

Obviously not all traits should be derived to the same code, because they are different traits after all. However, some of the semantics of the traits overlap a lot, so they have been grouped in the following way:

  1. From, only contains From.
  2. Into, only contains Into.
  3. Constructor, this doesn't derive a trait, but it derives a new method that can be used as a constructor.
  4. Not-like, contains Not and Neg.
  5. Add-like, contains Add, Sub, BitAnd, BitOr and BitXor.
  6. AddAssign-like, contains AddAssign, SubAssign, BitAndAssign, BitOrAssign and BitXorAssign.
  7. Mul-like, contains Mul, Div, Rem, Shr and Shl.
  8. MulAssign-like, contains MulAssign, DivAssign, RemAssign, ShrAssign and ShlAssign.

Generated code

It is important to understand what code gets generated when using one of the derives from this crate. That is why the links below explain what code gets generated for a trait for each group from before.

  1. #[derive(From)]
  2. #[derive(Into)]
  3. #[derive(Constructor)]
  4. #[derive(Not)]
  5. #[derive(Add)]
  6. #[derive(AddAssign)]
  7. #[derive(Mul)]
  8. #[derive(MulAssign)]

If you want to be sure what code is generated for your specific type I recommend using the cargo-expand utility. This will show you your code with all macros and derives expanded.

Installation

This library requires Rust 1.15 or higher, so this needs to be installed. Then add the following to Cargo.toml:

[dependencies]
derive_more = "0.6.0"

And this to the top of your Rust file:

#[macro_use]
extern crate derive_more;