![Build](https://github.com/colin-kiegel/rust-derive-builder/workflows/Build/badge.svg) [![Rust version](https://img.shields.io/badge/rust-1.56+-blue.svg)]() [![Documentation](https://docs.rs/derive_builder/badge.svg)](https://docs.rs/derive_builder) [![Latest version](https://img.shields.io/crates/v/derive_builder.svg)](https://crates.io/crates/derive_builder) [![All downloads](https://img.shields.io/crates/d/derive_builder.svg)](https://crates.io/crates/derive_builder) [![Downloads of latest version](https://img.shields.io/crates/dv/derive_builder.svg)](https://crates.io/crates/derive_builder) # Builder Pattern Derive [Rust][rust] macro to automatically implement the **builder pattern** for arbitrary structs. A simple `#[derive(Builder)]` will generate a `FooBuilder` for your struct `Foo` with all setter-methods and a build method. ## How it Works ```rust use derive_builder::Builder; #[derive(Default, Builder, Debug)] #[builder(setter(into))] struct Channel { token: i32, special_info: i32, // .. a whole bunch of other fields .. } fn main() { // builder pattern, go, go, go!... let ch = ChannelBuilder::default() .special_info(42u8) .token(19124) .build() .unwrap(); println!("{:?}", ch); } ``` Note that we did not write any definition or implementation of `ChannelBuilder`. Instead the `derive_builder` crate acts on `#[derive(Builder)]` and generates the necessary code at compile time. This is the generated boilerplate code you didn't need to write. :-) ```rust,ignore #[derive(Clone, Default)] struct ChannelBuilder { token: Option, special_info: Option, } #[allow(dead_code)] impl ChannelBuilder { pub fn token>(&mut self, value: VALUE) -> &mut Self { let mut new = self; new.token = Some(value.into()); new } pub fn special_info>(&mut self, value: VALUE) -> &mut Self { let mut new = self; new.special_info = Some(value.into()); new } fn build( &self, ) -> Result { Ok(Channel { id: match self.id { Some(ref value) => Clone::clone(value), None => { return Err( Into::into( ::derive_builder::UninitializedFieldError::from("id"), ), ) } }, token: match self.token { Some(ref value) => Clone::clone(value), None => { return Err( Into::into( ::derive_builder::UninitializedFieldError::from("token"), ), ) } }, special_info: match self.special_info { Some(ref value) => Clone::clone(value), None => { return Err( Into::into( ::derive_builder::UninitializedFieldError::from("special_info"), ), ) } }, }) } } ``` _Note: This is edited for readability. The generated code doesn't assume traits such as `Into` are in-scope, and uses full paths to access them._ ## Get Started It's as simple as three steps: 1. Add `derive_builder` to your `Cargo.toml` either manually or with [cargo-edit](https://github.com/killercup/cargo-edit): - `cargo add derive_builder` 2. Add `use derive_builder::Builder;` 3. Annotate your struct with `#[derive(Builder)]` ## Usage and Features - **Chaining**: The setter calls can be chained, because they consume and return `&mut self` by default. - **Builder patterns**: You can opt into other builder patterns by preceding your struct (or field) with `#[builder(pattern = "owned")]` or `#[builder(pattern = "immutable")]`. - **Extensible**: You can still define your own implementations for the builder struct and define additional methods. Just make sure to name them differently than the setter and build methods. - **Documentation and attributes**: Setter methods can be documented by simply documenting the corresponding field. Similarly `#[cfg(...)]` and `#[allow(...)]` attributes are also applied to the setter methods. - **Hidden fields**: You can skip setters via `#[builder(setter(skip))]` on each field individually. - **Setter visibility**: You can opt into private setter by preceding your struct with `#[builder(private)]`. - **Setter type conversions**: With `#[builder(setter(into))]`, setter methods will be generic over the input types – you can then supply every argument that implements the [`Into`][into] trait for the field type. - **Setter strip option**: With `#[builder(setter(strip_option))]`, setter methods will take `T` as parameter'type for field of type `Option`. - **Collection setters**: Adding `#[builder(setter(each(name = "method_name")))]` to fields whose types implement `Default` and `Extend` will generate a setter which adds items to the builder collection for that field. It's possible for these setters to be generic over the `Into` trait too, like so: `#[builder(setter(each(name = "foo", into)))]`. - **Builder field visibility**: You can use `#[builder(field(private))]` or `..(public)`, to set field visibility of your builder. - **Generic structs**: Are also supported, but you **must not** use a type parameter named `VALUE`, if you also activate setter type conversions. - **Default values**: You can use `#[builder(default)]` to delegate to the `Default` implementation or any explicit value via ` = ".."`. This works both on the struct and field level. - **Pre-build validation**: You can use `#[builder(build_fn(validate = "path::to::fn"))]` to add your own validation before the target struct is generated. - **Build method suppression**: You can use `#[builder(build_fn(skip))]` to disable auto-implementation of the build method and provide your own. - **Custom build method error types**: You can use `#[builder(build_fn(error = "path::to::Error"))]` to have your builder return an error type of your choosing. By default, the macro will emit an error type alongside the builder. - **Builder derivations**: You can use `#[builder(derive(Trait1, Trait2, ...))]` to have the builder derive additonal traits. All builders derive `Default` and `Clone`, so you should not declare those in this attribute. - **Pass-through attributes**: Use `#[builder_struct_attr(...)]`, `#[builder_impl_attr(...)]`, `#[builder_field_attr(...)]`, and `#[builder_setter_attr(...)]` to declare attributes that will be added to the relevant part of the generated builder. - **no_std support**: Just add `#[builder(no_std)]` to your struct, use feature `alloc`, and add `extern crate alloc` to your crate. - **No alloc no_std support**: Do not use `alloc` feature and then either add `#[builder(no_std, build_fn(error(validation_error = false)))]` or `#[builder(no_std, build_fn(error = "path::to::Error"))]` to your struct. - **Renaming and re-export support**: Use `#[builder(crate = "...")]` to set the root for `derive_builder`. This is useful if you want to rename `derive_builder` in `Cargo.toml` or if your crate is re-exporting `derive_builder::Builder` and needs the generated code to not directly reference the `derive_builder` crate. For more information and examples please take a look at our [documentation][doc]. ## Gotchas - Tuple structs and unit structs are not supported as they have no field names. We do not intend to support them. - When defining a generic struct, you cannot use `VALUE` as a generic parameter as this is what all setters are using. ## [Documentation][doc] Detailed explaination of all features and tips for troubleshooting. You'll also find a discussion of different builder patterns. [doc]: https://colin-kiegel.github.io/rust-derive-builder [rust]: https://www.rust-lang.org/ [builder-pattern]: https://aturon.github.io/ownership/builders.html [into]: https://doc.rust-lang.org/nightly/std/convert/trait.Into.html ## [Changelog](CHANGELOG.md) Yes, we keep a changelog. ## License Licensed under either of - Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or ) - MIT license ([LICENSE-MIT](LICENSE-MIT) or ) at your option. ### Contribution Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.