bauer

Bauer is a crate for automatically generating Builder-patterns for your structs!

Not sure what kind of builder you want? Bauer supports a variety of sub-patterns: Owned, Borrowed, and even Type-State!

Examples

#[derive(Builder)]
#[builder(kind = "type-state")]
pub struct Foo {
    required_field: u32,
    #[builder(default)]
    default_field: u32,
    #[builder(into)]
    converting_field: String,
    #[builder(repeat)]
    repeating_field: Vec<u32>,
    #[builder(repeat, repeat_n = 1..=3)]
    limited_repeating_field: Vec<u32>,
}

let foo: Foo = Foo::builder()
    .required_field(42)
    // .default_field(69) // defaults to 0
    .converting_field("hello world") // calls `.into()` to convert from &str -> String
    .repeating_field(420)
    .repeating_field(1337)
    .limited_repeating_field(0) // If not called 1..=3 times, this will fail
    .build();

Check out the repository for more examples!

Configuration

Builders are very configurable. A few of the biggest features can be found below. For a more comprehensive collection of features, look at the Builder macro.

Kinds

Bauer supports generating 3 kinds of builders:

Owned (default) / Borrowed

"owned" builders are passed around by value and "borrowed" builders are passed by mutable reference.

Type-State

"type-state" builders use the type-state pattern and generate builds that are validated at compile-time using the type system.

Builder kinds can be switched between trivially using #[builder(kind = <kind>)] on the struct.

Field Attributes

These attributes go in #[builder(..)] on individual fields of the structure

default

Specify a default value for the field to have, or use [Default::default]

repeat

Allow any structure which supports [FromIterator] to be specified by calling the function multiple times. If repeat_n is specified, the number of times to repeat is limited.

into/tuple/adapter

Change how the generated builder function handles input. Can also be used with repeat.

• into will make the function accepet impl Into<T>
• tuple will make the function accept each item as a separate argument
• adapter can specify each argument and how they should be converted into the value

There are many more attributes, all can be found on the Builder macro.