typed-builder 0.16.2

Compile-time type-checked builder derive
Documentation 
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use typed_builder::TypedBuilder;

#[derive(Debug, PartialEq, TypedBuilder)]
struct Foo {
    // Mandatory Field:
    x: i32,

    // #[builder(default)] without parameter - use the type's default
    // #[builder(setter(strip_option))] - wrap the setter argument with `Some(...)`
    #[builder(default, setter(strip_option))]
    y: Option<i32>,

    // Or you can set the default
    #[builder(default = 20)]
    z: i32,
}

fn main() {
    assert_eq!(Foo::builder().x(1).y(2).z(3).build(), Foo { x: 1, y: Some(2), z: 3 });

    // Change the order of construction:
    assert_eq!(Foo::builder().z(1).x(2).y(3).build(), Foo { x: 2, y: Some(3), z: 1 });

    // Optional fields are optional:
    assert_eq!(Foo::builder().x(1).build(), Foo { x: 1, y: None, z: 20 });

    // This will not compile - because we did not set x:
    // Foo::builder().build();

    // This will not compile - because we set y twice:
    // Foo::builder().x(1).y(2).y(3);
}