Derive Macro Default 

#[derive(Default)]
{
    // Attributes available to this derive:
    #[default]
}

Derives Default with more flexibility than Rust’s built-in #[derive(Default)].

In addition to the functionality allowed by the built-in #[derive(Default)], this version allows:

• overriding the default values for particular fields using #[default = ...] or #[default(...)]; and
• using #[default] on a non-unit enum variant

Examples

Structs

#[derive(derive_extras::Default)]
struct ExampleStruct {
    x: i32,
    #[default = 15]
    y: i32,
    z: i32,
}

For this struct, the following Default implementation is derived:

impl Default for ExampleStruct {
    fn default() -> Self {
        Self {
            x: Default::default(),
            y: 15,
            z: Default::default(),
        }
    }
}

Enums

#[derive(derive_extras::Default)]
enum ExampleEnum {
    Unit,
    Tuple(i32, i32, i32),

    #[default]
    Struct {
        x: i32,
        #[default = 15]
        y: i32,
        z: i32,
    },
}

For this enum, the following Default implementation is derived:

impl Default for ExampleEnum {
    fn default() -> Self {
        Self::Struct {
            x: Default::default(),
            y: 15,
            z: Default::default(),
        }
    }
}