[]()
[](https://docs.rs/derive_builder)
[](https://crates.io/crates/derive_builder)
[](https://crates.io/crates/derive_builder)
[](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
#[macro_use]
extern crate derive_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<i32>,
special_info: Option<i32>,
}
#[allow(dead_code)]
impl ChannelBuilder {
pub fn token<VALUE: Into<i32>>(&mut self, value: VALUE) -> &mut Self {
let mut new = self;
new.token = Some(value.into());
new
}
pub fn special_info<VALUE: Into<i32>>(&mut self, value: VALUE) -> &mut Self {
let mut new = self;
new.special_info = Some(value.into());
new
}
fn build(
&self,
) -> Result<Channel, ChannelBuilderError> {
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<T>`.
- **Collection setters**: Adding `#[builder(setter(each = "method_name"))]` to fields whose types implement `Default` and `Extend` will generate a setter which adds items to the builder collection for that field.
- **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.
- **no_std support**: Just add `#[builder(no_std)]` to your struct and add `extern crate alloc` to your crate.
For more information and examples please take a look at our [documentation][doc].
## Gotchas
- Renaming `derive_builder` in `Cargo.toml` is not supported.
- 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 <http://www.apache.org/licenses/LICENSE-2.0>)
- MIT license ([LICENSE-MIT](LICENSE-MIT) or <http://opensource.org/licenses/MIT>)
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.