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//! Derive a builder for a struct //! //! This crate implements the [builder pattern] for you. //! Just apply `#[derive(Builder)]` to a struct `Foo`, and it will derive an additional //! struct `FooBuilder` with **setter**-methods for all fields and a **build**-method //! — the way you want it. //! //! # Quick Start //! //! Add `derive_builder` as a dependency to you `Cargo.toml`. //! //! ## What you write //! //! ```rust //! #[macro_use] //! extern crate derive_builder; //! //! #[derive(Builder)] //! struct Lorem { //! ipsum: u32, //! // .. //! } //! # fn main() {} //! ``` //! //! ## What you get //! //! ```rust //! # #[macro_use] //! # extern crate derive_builder; //! # //! # struct Lorem { //! # ipsum: u32, //! # } //! # fn main() {} //! # //! #[derive(Clone, Default)] //! struct LoremBuilder { //! ipsum: Option<u32>, //! } //! //! #[allow(dead_code)] //! impl LoremBuilder { //! pub fn ipsum(&mut self, value: u32) -> &mut Self { //! let mut new = self; //! new.ipsum = Some(value); //! new //! } //! //! fn build(&self) -> Result<Lorem, String> { //! Ok(Lorem { //! ipsum: Clone::clone(self.ipsum //! .as_ref() //! .ok_or("ipsum must be initialized")?), //! }) //! } //! } //! ``` //! //! By default all generated setter-methods take and return `&mut self` //! (aka _non-conusuming_ builder pattern). Accordingly, the build method also takes a //! reference by default. //! //! You can easily opt into different patterns and control many other aspects. //! //! The build method returns `Result<T, String>`, where `T` is the struct you started with. //! It returns `Err` if you didn't initialize all fields and no default values were //! provided. //! //! # Builder Patterns //! //! Let's look again at the example above. You can now build structs like this: //! //! ```rust //! # #[macro_use] extern crate derive_builder; //! # #[derive(Builder)] struct Lorem { ipsum: u32 } //! # fn try_main() -> Result<(), String> { //! let x: Lorem = LoremBuilder::default().ipsum(42).build()?; //! # Ok(()) //! # } fn main() { try_main().unwrap(); } //! ``` //! //! Ok, _chaining_ method calls is nice, but what if `ipsum(42)` should only happen if `geek = true`? //! //! So let's make this call conditional //! //! ```rust //! # #[macro_use] extern crate derive_builder; //! # #[derive(Builder)] struct Lorem { ipsum: u32 } //! # fn try_main() -> Result<(), String> { //! # let geek = true; //! let mut builder = LoremBuilder::default(); //! if geek { //! builder.ipsum(42); //! } //! let x: Lorem = builder.build()?; //! # Ok(()) //! # } fn main() { try_main().unwrap(); } //! ``` //! //! Now it comes in handy that our setter methods take and return mutable references. Otherwise //! we would need to write something more clumsy like `builder = builder.ipsum(42)` to reassign //! the return value each time we have to call a setter conditionally. //! //! Setters with mutable references are therefore a convenient default for the builder //! pattern in Rust. //! //! But this is a free world and the choice is still yours! //! //! ## Owned, aka Consuming //! //! Precede your struct (or field) with `#[builder(pattern="owned")]` to opt into this pattern. //! //! * Setters take and return `self`. //! * PRO: Setter calls and final build method can be chained. //! * CON: If you don't chain your calls, you have to create a reference to each return value, //! e.g. `builder = builder.ipsum(42)`. //! //! ## Mutable, aka Non-Comsuming (recommended) //! //! This pattern is recommended and active by default if you don't specify anything else. //! You can precede your struct (or field) with `#[builder(pattern="mutable")]` //! to make this choice explicit. //! //! * Setters take and return `&mut self`. //! * PRO: Setter calls and final build method can be chained. //! * CON: The build method must clone or copy data to create something owned out of a //! mutable reference. Otherwise it could not be used in a chain. **(*)** //! //! ## Immutable //! //! Precede your struct (or field) with `#[builder(pattern="immutable")]` to opt into this pattern. //! //! * Setters take and return `&self`. //! * PRO: Setter calls and final build method can be chained. //! * CON: If you don't chain your calls, you have to create a reference to each return value, //! e.g. `builder = builder.ipsum(42)`. //! * CON: The build method _and each setter_ must clone or copy data to create something owned //! out of a reference. **(*)** //! //! ## (*) Performance Considerations //! //! Luckily Rust is clever enough to optimize these clone-calls away in release builds //! for your every-day use cases. Thats quite a safe bet - we checked this for you. ;-) //! Switching to consuming signatures (=`self`) is unlikely to give you any performance //! gain, but very likely to restrict your API for non-chained use cases. //! //! # More Features //! //! ## Hidden Fields //! //! You can hide fields by skipping their setters on the builder struct. //! //! - Opt-out — skip setters via `#[builder(setter(skip))]` on individual fields. //! - Opt-in — set `#[builder(setter(skip))]` on the whole struct //! and enable individual setters via `#[builder(setter)]`. //! //! The types of skipped fields must implement `Default`. //! //! ```rust //! # #[macro_use] //! # extern crate derive_builder; //! # //! #[derive(Builder)] //! struct SetterOptOut { //! setter_present: u32, //! #[builder(setter(skip))] //! setter_skipped: u32, //! } //! # fn main() {} //! ``` //! //! Alternatively, you can use the more verbose form: //! //! - `#[builder(setter(skip="true"))]` //! - `#[builder(setter(skip="false"))]` //! //! ## Setter Visibility //! //! Setters are public by default. You can precede your struct (or field) with `#[builder(public)]` //! to make this explicit. //! //! Otherwise precede your struct (or field) with `#[builder(private)]` to opt into private //! setters. //! //! ## Setter Prefixes //! //! Setter methods are named after their corresponding field by default. //! //! You can precede your struct (or field) with e.g. `#[builder(setter(prefix="xyz"))` to change //! the method name to `xyz_foo` if the field is named `foo`. Note that an underscore is included //! by default, since Rust favors snake case here. //! //! ## Generic Setters //! //! You can make each setter generic over the `Into`-trait. It's as simple as adding //! `#[builder(setter(into))]` to either a field or the whole struct. //! //! ```rust //! # #[macro_use] //! # extern crate derive_builder; //! # //! #[derive(Builder, Debug, PartialEq)] //! struct Lorem { //! #[builder(setter(into))] //! pub ipsum: String, //! } //! //! fn main() { //! // `"foo"` will be converted into a `String` automatically. //! let x = LoremBuilder::default().ipsum("foo").build().unwrap(); //! //! assert_eq!(x, Lorem { //! ipsum: "foo".to_string(), //! }); //! } //! ``` //! //! ## Default Values //! //! You can define default values for each field via annotation by `#[builder(default="...")]`, //! where `...` stands for any Rust expression and must be string-escaped, e.g. //! //! * `#[builder(default="42")]` //! * `#[builder(default)]` delegates to the [`Default`] trait of the base type. //! //! The expression will be evaluated with each call to `build`. //! //! ```rust //! # #[macro_use] //! # extern crate derive_builder; //! # //! #[derive(Builder, Debug, PartialEq)] //! struct Lorem { //! #[builder(default="42")] //! pub ipsum: u32, //! } //! //! fn main() { //! // If we don't set the field `ipsum`, //! let x = LoremBuilder::default().build().unwrap(); //! //! // .. the custom default will be used for `ipsum`: //! assert_eq!(x, Lorem { //! ipsum: 42, //! }); //! } //! ``` //! //! ### Tips //! //! * The `#[builder(default)]` annotation can be used on the struct level, too. Overrides are //! still possible. //! * Delegate to a private helper method on `FooBuilder` for anything fancy. This way //! you will get _much better error diagnostics_ from the rust compiler and it will be _much //! more readable_ for other human beings. :-) //! //! [`Default`]: https://doc.rust-lang.org/std/default/trait.Default.html //! //! ```rust //! # #[macro_use] //! # extern crate derive_builder; //! # //! # #[derive(Builder, PartialEq, Debug)] //! struct Lorem { //! ipsum: String, //! // Custom defaults can delegate to helper methods //! // and pass errors to the enclosing `build()` method via `?`. //! #[builder(default="self.default_dolor()?")] //! dolor: String, //! } //! //! impl LoremBuilder { //! // Private helper method with access to the builder struct. //! fn default_dolor(&self) -> Result<String, String> { //! match self.ipsum { //! Some(ref x) if x.chars().count() > 3 => Ok(format!("dolor {}", x)), //! _ => Err("ipsum must at least 3 chars to build dolor".to_string()), //! } //! } //! } //! //! # fn main() { //! # let x = LoremBuilder::default() //! # .ipsum("ipsum".to_string()) //! # .build() //! # .unwrap(); //! # //! # assert_eq!(x, Lorem { //! # ipsum: "ipsum".to_string(), //! # dolor: "dolor ipsum".to_string(), //! # }); //! # } //! ``` //! //! You can even reference other fields, but you have to remember that the builder struct //! will wrap every type in an Option ([as illustrated earlier](#what-you-get)). //! //! ## Generic Structs //! //! ```rust //! # #[macro_use] //! # extern crate derive_builder; //! # //! #[derive(Builder, Debug, PartialEq, Default, Clone)] //! struct GenLorem<T: Clone> { //! ipsum: &'static str, //! dolor: T, //! } //! //! fn main() { //! let x = GenLoremBuilder::default().ipsum("sit").dolor(42).build().unwrap(); //! assert_eq!(x, GenLorem { ipsum: "sit".into(), dolor: 42 }); //! } //! ``` //! //! ## Documentation Comments and Attributes //! //! `#[derive(Builder)]` copies doc comments and attributes (`#[...]`) from your fields //! to the according builder fields and setter-methods, if it is one of the following: //! //! * `/// ...` //! * `#[doc = ...]` //! * `#[cfg(...)]` //! * `#[allow(...)]` //! //! The whitelisting minimizes interference with other custom attributes like //! those used by Serde, Diesel, or others. //! //! ```rust //! # #[macro_use] //! # extern crate derive_builder; //! # //! #[derive(Builder)] //! struct Lorem { //! /// `ipsum` may be any `String` (be creative). //! ipsum: String, //! #[doc = r"`dolor` is the estimated amount of work."] //! dolor: i32, //! // `#[derive(Builder)]` understands conditional compilation via cfg-attributes, //! // i.e. => "no field = no setter". //! #[cfg(target_os = "macos")] //! #[allow(non_snake_case)] //! Im_a_Mac: bool, //! } //! # fn main() {} //! ``` //! //! # **`#![no_std]`** Support (on Nightly) //! //! You can activate support for `#![no_std]` by adding `#[builder(no_std)]` to your struct //! and `#![feature(collections)] extern crate collections` to your crate. //! //! The latter requires the _nightly_ toolchain. //! //! # Troubleshooting //! //! ## Gotchas //! //! - Tuple structs and unit structs are not supported as they have no field //! names. //! - Generic setters introduce a type parameter `VALUE: Into<_>`. Therefore you can't use //! `VALUE` as a type parameter on a generic struct in combination with generic setters. //! - When re-exporting the underlying struct under a different name, the //! auto-generated documentation will not match. //! - If derive_builder depends on your crate, and vice versa, then a cyclic //! dependency would occur. To break it you could try to depend on the //! [`derive_builder_core`] crate instead. //! //! ## Debugging Info //! //! If you experience any problems during compilation, you can enable additional debug output in //! two steps: //! //! 1. Add `features = ["logging"]` to the `derive_builder` dependency in `Cargo.toml`. //! 2. Set this environment variable before calling cargo or rustc `RUST_LOG=derive_builder=trace`. //! //! Example: `env RUST_LOG=derive_builder=trace cargo test`. //! //! ## Report Issues and Ideas //! //! [Open an issue on GitHub](https://github.com/colin-kiegel/rust-derive-builder/issues) //! //! If possible please try to provide the debugging info if you experience unexpected //! compilation errors (see above). //! //! [builder pattern]: https://aturon.github.io/ownership/builders.html //! [`derive_builder_core`]: https://crates.io/crates/derive_builder_core #![crate_type = "proc-macro"] #![deny(warnings)] extern crate proc_macro; extern crate syn; #[macro_use] extern crate quote; #[cfg(feature = "logging")] #[macro_use] extern crate log; #[cfg(feature = "logging")] extern crate env_logger; extern crate derive_builder_core; #[cfg(not(feature = "logging"))] #[macro_use] mod log_disabled; mod options; use proc_macro::TokenStream; #[cfg(feature = "logging")] use std::sync::{Once, ONCE_INIT}; use options::{struct_options_from, field_options_from}; #[cfg(feature = "logging")] static INIT_LOGGER: Once = ONCE_INIT; #[doc(hidden)] #[proc_macro_derive(Builder, attributes(builder))] pub fn derive(input: TokenStream) -> TokenStream { #[cfg(feature = "logging")] INIT_LOGGER.call_once(|| { env_logger::init().unwrap(); }); let input = input.to_string(); let ast = syn::parse_macro_input(&input).expect("Couldn't parse item"); let result = builder_for_struct(ast).to_string(); debug!("generated tokens: {}", result); result.parse().expect(&format!("Couldn't parse `{}` to tokens", result)) } fn builder_for_struct(ast: syn::MacroInput) -> quote::Tokens { debug!("Deriving Builder for `{}`.", ast.ident); let (opts, field_defaults) = struct_options_from(&ast); let fields = match ast.body { syn::Body::Struct(syn::VariantData::Struct(fields)) => fields, _ => panic!("`#[derive(Builder)]` can only be used with braced structs"), }; let mut builder = opts.as_builder(); let mut build_fn = opts.as_build_method(); builder.doc_comment(format!(include_str!("doc_tpl/builder_struct.md"), struct_name = ast.ident.as_ref())); build_fn.doc_comment(format!(include_str!("doc_tpl/builder_method.md"), struct_name = ast.ident.as_ref())); for f in fields { let f_opts = field_options_from(f, &field_defaults); builder.push_field(f_opts.as_builder_field()); builder.push_setter_fn(f_opts.as_setter()); build_fn.push_initializer(f_opts.as_initializer()); } builder.push_build_fn(build_fn); quote!(#builder) }