builder_type

Applies to: structs functions methods

Overrides name, visibility and docs for the builder struct.

Short syntax configures just the name.

#[builder(builder_type = CustomName)]

Long syntax provides more flexibility. All keys are optional.

#[builder(
    builder_type(
        name = CustomName,
        vis = "pub(crate)",
        doc {
            /// Custom docs
        }
    )
)]

name

The default name for the builder struct is chosen according to the following rules:

Syntax	Default
struct T	{T}Builder
Associated fn T::new/builder()	{T}Builder
Associated fn T::fn_name()	{T}{FnName}Builder
Free fn fn_name()	{FnName}Builder

vis

The visibility must be enclosed with quotes. Use "" or "pub(self)" for private visibility.

The default visibility is the same as the visibility of the underlying struct or fn.

doc

Simple documentation is generated by default. The syntax of this attribute expects a block with doc comments.

doc {
    /// Doc comments
}

Examples

Struct

use bon::Builder;

#[derive(Builder)]
#[builder(builder_type = MyBuilder)] 
struct Brush {}

let builder: MyBuilder = Brush::builder();

Function

use bon::builder;

#[builder(builder_type = MyBuilder)] 
fn brush() {}

let builder: MyBuilder = brush();

Method

use bon::bon;

struct Brush;

#[bon]
impl Brush {
    #[builder(builder_type = MyBuilder)] 
    fn new() -> Self {
        Self
    }
}

let builder: MyBuilder = Brush::builder();

---

You'll usually want to override the builder type name when you already have such a name in scope. For example, if you have a struct and a function with the same name both annotated with #[derive(Builder)] and #[builder]:

Errored

use bon::{builder, Builder};

#[derive(Builder)] 
struct Brush {}

#[builder] 
fn brush() {}

// `BrushBuilder` builder type name was generated for both
// the struct and the function. This is a compile error
let builder: BrushBuilder = Brush::builder();
let builder: BrushBuilder = brush();

Fixed

use bon::{builder, Builder};

#[derive(Builder)]
#[builder(builder_type = MyBuilder)] 
struct Brush {}

#[builder]
fn brush() {}

// Now builder types are named differently
let builder: MyBuilder = Brush::builder();
let builder: BrushBuilder = brush();