Derives for Builders

You can specify some extra derives on the generated builder struct itself via the top-level #[builder(derive(...))] attribute.

For example, if you want to inspect the values set in the builder for debugging purposes, you can derive the Debug trait for your builder.

Struct

#[derive(bon::Builder)]
#[builder(derive(Debug))] 
struct Example {
    name: String,
    is_admin: bool,
    level: Option<u32>,
}

let builder = Example::builder().name("Bon".to_owned());

// This will output the current state of the builder to `stderr`
dbg!(&builder);

// You can also format the debug output to `String`:
assert_eq!(
    format!("{builder:?}"),
    // Only the fields that were set will be output
    r#"ExampleBuilder { name: "Bon" }"#
);

// Finish building
builder.is_admin(true).build();

Function

#[bon::builder(derive(Debug))] 
fn example(
    name: String,
    is_admin: bool,
    level: Option<u32>,
) {}

let builder = example().name("Bon".to_owned());

// This will output the current state of the builder to `stderr`
dbg!(&builder);

// You can also format the debug output to `String`:
assert_eq!(
    format!("{builder:?}"),
    // Only the fields that were set will be output
    r#"ExampleBuilder { name: "Bon" }"#
);

// Finish building
builder.is_admin(true).call();

Method

struct Example;

#[bon::bon]
impl Example {
    #[builder(derive(Debug))] 
    fn method(
        name: String,
        is_admin: bool,
        level: Option<u32>,
    ) {}
}

let builder = Example::method().name("Bon".to_owned());

// This will output the current state of the builder to `stderr`
dbg!(&builder);

// You can also format the debug output to `String`:
assert_eq!(
    format!("{builder:?}"),
    // Only the fields that were set will be output
    r#"ExampleMethodBuilder { name: "Bon" }"#
);

// Finish building
builder.is_admin(true).call();

You can also derive the Clone and Into traits for your builder using this same attribute. See more details in the reference for the #[builder(derive(...))] attribute.