bon

# Overview `bon` is a Rust crate for generating compile-time-checked builders for structs and functions. It also provides idiomatic partial application with optional and named parameters for functions and methods. If you wonder "Why would I use builders?", see the [motivational blog post](https://bon-rs.com/blog/how-to-do-named-function-arguments-in-rust). ## Function Builder You can turn a function with positional parameters into a function with named parameters with `#[builder]`. ```rust use bon::builder; #[builder] fn greet(name: &str, level: Option) -> String { let level = level.unwrap_or(0); format!("Hello {name}! Your level is {level}") } let greeting = greet() .name("Bon") .level(24) // <- setting `level` is optional, we could omit it .call(); assert_eq!(greeting, "Hello Bon! Your level is 24"); ``` Any syntax for functions is supported including `async`, fallible, generic functions, `impl Trait`, etc. Many things are customizable with additional attributes described in the [API reference](https://bon-rs.com/reference/builder), but let's see what else `bon` has to offer. ## Struct Builder Use `#[derive(Builder)]` to generate a builder for a struct. ```rust use bon::Builder; #[derive(Builder)] struct User { name: String, is_admin: bool, level: Option, } let user = User::builder() .name("Bon".to_owned()) // `level` is optional, we could omit it here .level(24) // call setters in any order .is_admin(true) .build(); assert_eq!(user.name, "Bon"); assert_eq!(user.level, Some(24)); assert!(user.is_admin); ``` ## Method Builder Associated methods require `#[bon]` on top of the impl block additionally. ### Method `new` The method named `new` generates `builder()/build()` methods. ```rust use bon::bon; struct User { id: u32, name: String, } #[bon] impl User { #[builder] fn new(id: u32, name: String) -> Self { Self { id, name } } } let user = User::builder() .id(1) .name("Bon".to_owned()) .build(); assert_eq!(user.id, 1); assert_eq!(user.name, "Bon"); ``` `#[derive(Builder)]` on a struct generates builder API that is fully compatible with placing `#[builder]` on the `new()` method with a signature similar to the struct's fields (more details on the [Compatibility](https://bon-rs.com/guide/basics/compatibility#switching-between-derive-builder-and-builder-on-the-new-method) page). ### Other Methods All other methods generate `{method_name}()/call()` methods. ```rust use bon::bon; struct Greeter { name: String, } #[bon] impl Greeter { #[builder] fn greet(&self, target: &str, prefix: Option<&str>) -> String { let prefix = prefix.unwrap_or("INFO"); let name = &self.name; format!("[{prefix}] {name} says hello to {target}") } } let greeter = Greeter { name: "Bon".to_owned() }; let greeting = greeter .greet() .target("the world") // `prefix` is optional, omitting it is fine .call(); assert_eq!(greeting, "[INFO] Bon says hello to the world"); ``` Methods with or without `self` are both supported. ## No Panics Possible Builders generated by `bon`'s macros use the typestate pattern to ensure all required parameters are filled, and the same setters aren't called repeatedly to prevent unintentional overwrites. If something is wrong, a compile error will be created. | ⭐ Don't forget to give our repo a [star on Github ⭐](https://github.com/elastio/bon)! | | --------------------------------------------------------------------------------------- | ## What's Next? What you've seen above is the first page of the Guide Book. If you want to learn more, jump to the [Basics](https://bon-rs.com/guide/basics) section. And remember: knowledge is power ! Feel free to jump to code and use the `#[builder]` and `#[derive(Builder)]` once you've seen enough docs to get started. The [ API Reference](https://bon-rs.com/reference/builder) will help you navigate the attributes once you feel comfortable with the basics of `bon`. Both `#[derive(Builder)]` on structs and `#[builder]` on functions/methods have almost identical attributes API, so the documentation for them is common. ## Installation Add `bon` to your `Cargo.toml`. ```toml [dependencies] bon = "3.10" ``` You can opt out of `std` and `alloc` cargo features with `default-features = false` for `no_std` environments. See [alternatives](https://bon-rs.com/guide/alternatives) for comparison. ## Getting Help If you can't figure something out, consult the docs and maybe use the ` Search` bar on our [docs website](https://bon-rs.com). You may also create an issue or a discussion on the [Github repository](https://github.com/elastio/bon) for help or write us a message on [Discord](https://bon-rs.com/discord). ## Socials

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## Acknowledgments This project was heavily inspired by such awesome crates as [`buildstructor`](https://docs.rs/buildstructor), [`typed-builder`](https://docs.rs/typed-builder) and [`derive_builder`](https://docs.rs/derive_builder). This crate was designed with many lessons learned from them. ## Past Supporters ## License Licensed under either of Apache License, Version 2.0 or MIT license at your option.
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.