README.md

derive_more

Rust has lots of builtin traits that are implemented for its basic types, such as Add, Not, From or Display. 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:

use derive_more::{Add, Display, From, Into};

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

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

#[derive(PartialEq, From, Add, Display)]
enum MyEnum {
    #[display("int: {_0}")]
    Int(i32),
    Uint(u32),
    #[display("nothing")]
    Nothing,
}

assert!(MyInt(11) == MyInt(5) + 6.into());
assert!((5, 6) == Point2D { x: 5, y: 6 }.into());
assert!(MyEnum::Int(15) == (MyEnum::Int(8) + 7.into()).unwrap());
assert!(MyEnum::Int(15).to_string() == "int: 15");
assert!(MyEnum::Uint(42).to_string() == "42");
assert!(MyEnum::Nothing.to_string() == "nothing");

The derivable traits

Below are all the traits that you can derive using this library. Some trait derivations are so similar that the further documentation will only show a single one of them. You can recognize these by the "-like" suffix in their name. The trait name before that will be the only one that is used throughout the further documentation.

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.

You can use the cargo-expand utility to see the exact code that is generated for your specific type. This will show you your code with all macros and derives expanded.

NOTE: You still have to derive each trait separately. So #[derive(Mul)] doesn't automatically derive Div as well. To derive both you should do #[derive(Mul, Div)]

Conversion traits

These are traits that are used to convert automatically between types.

1. From
2. Into
3. FromStr
4. TryFrom
5. TryInto
6. IntoIterator
7. AsRef, AsMut

Formatting traits

These traits are used for converting a struct to a string in different ways.

1. Debug
2. Display-like, contains Display, Binary, Octal, LowerHex, UpperHex, LowerExp, UpperExp, Pointer

Error-handling traits

These traits are used to define error-types.

1. Error

Operators

These are traits that can be used for operator overloading.

1. Index
2. Deref
3. Not-like, contains Not and Neg
4. Add-like, contains Add, Sub, BitAnd, BitOr, BitXor
5. Mul-like, contains Mul, Div, Rem, Shr and Shl
6. Sum-like, contains Sum and Product
7. IndexMut
8. DerefMut
9. AddAssign-like, contains AddAssign, SubAssign, BitAndAssign, BitOrAssign and BitXorAssign
10. MulAssign-like, contains MulAssign, DivAssign, RemAssign, ShrAssign and ShlAssign

Static methods

These don't derive traits, but derive static methods instead.

1. Constructor, this derives a new method that can be used as a constructor. This is very basic if you need more customization for your constructor, check out the derive-new crate.
2. IsVariant, for each variant foo of an enum type, derives a is_foo method.
3. Unwrap, for each variant foo of an enum type, derives an unwrap_foo method.
4. TryUnwrap, for each variant foo of an enum type, derives an try_unwrap_foo method.

Re-exports

This crate also re-exports all the standard library traits, that it adds derives for, in the with_trait module. So, both the Display derive and the Display trait will be in scope when you add the following code:

use derive_more::with_trait::Display; // also imports `core::fmt::Display`

By default, derive macros only, without the corresponding traits, are imported from the crate's root (or from the derive module):

use derive_more::Display;   // imports macro only
use derive_more::derive::*; // imports all macros only

Hygiene

For hygiene purposes, macros use derive_more::* absolute paths in their expansions. This might introduce a trouble, if you want to re-export derive_more macros in your own crate without using the derive_more as a direct dependency in downstream crates:

use my_lib::Display; // re-exported in `my_lib` crate

#[derive(Display)] // error: could not find `derive_more` in the list of imported crates
struct MyInt(i32);

In such case, you should re-export the derive_more module too:

use my_lib::{derive_more, Display}; // re-exported in `my_lib` crate

#[derive(Display)] // works fine now!
struct MyInt(i32);

Installation

To avoid redundant compilation times, by default no derives are supported. You have to enable each type of derive as a feature in Cargo.toml:

[dependencies]
# You can specify the types of derives that you need for less time spent
# compiling. For the full list of features see this crate its `Cargo.toml`.
derive_more = { version = "1", features = ["from", "add", "into_iterator"] }

[dependencies]
# If you don't care much about compilation times and simply want to have
# support for all the possible derives, you can use the "full" feature.
derive_more = { version = "1", features = ["full"] }

[dependencies]
# If you run in a `no_std` environment you should disable the default features,
# because the only default feature is the "std" feature.
# NOTE: You can combine this with "full" feature to get support for all the
#       possible derives in a `no_std` environment.
derive_more = { version = "1", default-features = false }

And this to the top of your Rust file:

// use the derives that you want in the file
use derive_more::{Add, Display, From};

If you're still using Rust 2015, add this instead:

extern crate core;
#[macro_use]
extern crate derive_more;
# fn main() {} // omit wrapping statements above into `main()` in tests

MSRV policy

This library requires Rust 1.75 or higher.

Changing MSRV (minimum supported Rust version) of this crate is treated as a minor version change in terms of Semantic Versioning.

• So, if MSRV changes are NOT concerning for your project, just use the default caret requirement:

  [dependencies]
  derive_more = "1" # or "1.0", or "^1.0"

• However, if MSRV changes are concerning for your project, then use the tilde requirement to pin to a specific minor version:

  [dependencies]
  derive_more = "~1.0" # or "~1.0.0"