Attribute Macro staged_builder::staged_builder

#[staged_builder]

Creates a staged builder interface for structs.

The macro will create a submodule with the snake_case version of the type’s name containing the builder types, and add a builder constructor function to the type. Each required field of the struct will correspond to a builder type named after it, with an additional “final” stage to set optional fields and construct the final value.

By default, all fields are considered required and their setters will simply take their declared type by-value. This behavior can be customized with field options.

Field options

Options can be applied to individual fields via the #[builder(...)] attribute as a comma-separated sequence:

• into - Causes the setter method for the field to take impl Into<FieldType> rather than FieldType directly.
• default - Causes the field to be considered optional. The Default trait is normally used to generate the default field value. A custom default can be specified with default = <expr>, where <expr> is an expression.

Example expansion

use staged_builder::staged_builder;

#[staged_builder]
pub struct MyStruct {
    required_field: u32,
    #[builder(into)]
    into_required_field: String,
    #[builder(default)]
    standard_optional_field: bool,
    #[builder(default = "foobar".to_string())]
    custom_default_field: String,
}

Will expand into:

pub struct MyStruct {
    required_field: u32,
    into_required_field: String,
    standard_optional_field: bool,
    custom_default_field: i32,
}

impl MyStruct {
    pub fn builder() -> my_struct::BuilderRequiredFieldStage {
        // ...
    }
}

pub struct my_struct {
    pub struct BuilderRequiredFieldStage {}

    impl BuilderRequiredFieldStage {
        pub fn required_field(self, required_field: u32) -> BuilderIntoRequiredFieldStage {
            // ...
        }
    }

    pub struct BuilderIntoRequiredFieldStage {
        // ...
    }

    impl BuilderIntoRequiredFieldStage {
        pub fn into_required_field(self, into_required_field: impl Into<String>) -> BuilderFinal {
            // ...
        }
    }

    pub struct BuilderFinal {
        // ...
    }

    impl BuilderFinal {
        pub fn standard_optional_field(self, standard_optional_field: bool) -> Self {
            // ...
        }

        pub fn custom_default_field(self, custom_default_field: String) -> Self {
            // ...
        }

        pub fn build(self) -> super::MyStruct {
            // ...
        }
    }
}