derive_less

A library for generating #[...] and pub code in item declarations.

Example

Suppose you needed the following code:

#[derive(Debug)]
pub struct Foo(
    #[apple]
    pub i32,
    #[apple]
    pub i32,
);
#[derive(Clone)]
pub enum Bar {
    #[orange]
    X(i32),
    #[orange]
    Y(i32),
}
#[derive(Debug)]
pub struct Baz(
    #[apple]
    pub i32,
    #[apple]
    pub f32,
    #[apple]
    pub i32,
);
#[derive(Clone)]
pub enum Qux {
    #[orange]
    A(i32),
    #[orange]
    B(i32),
    #[orange]
    C(i32),
}

Instead of typing out #[orange], #[apple], and pub, repeatedly for each item declaration, you could simply write:

use derive_less::derive_less;

derive_less! {
    #[derive(Debug)] pub struct ... { #[apple] pub ...  }
    #[derive(Clone)] pub enum   ... { #[orange]    ...  }

    struct Foo(i32, i32);
    enum Bar {
        X(i32),
        Y(i32),
    }
    struct Baz(i32, f32, i32);
    enum Qux {
        A(i32),
        B(i32),
        C(i32),
    }
}

You can also mix in derives that only apply to certain items/variants/fields, e.g:

use derive_less::derive_less;

derive_less! {
    #[derive(Debug)] pub struct ... { #[apple] pub ...  }
    #[derive(Clone)] pub enum   ... { #[orange]    ...  }

    struct Foo(i32, i32);
    enum Bar {
        X(#[peanut] i32),
        Y(i32),
    }
    #[derive(PartialEq, PartialOrd)]
    struct Baz(i32, f32, i32);
    enum Qux {
        A(i32),
        B(i32),
        C(i32),
    }
}

Limitations

Currently only supports:

• Tuple structs
• Unit structs
• Regular structs
• Enums with unnamed or unit fields
• Enums with (only) named fields

While structs and enums can take multiple #[...], e.g.:

#[hello] #[world] struct ... { ...  }

Fields and variants accept at most one #[...] due to current restrictions in macro_rules!. In other words, this does not work at the moment:

struct ... { #[hello] #[world] ...  }

Future work

Handle more cases by either rewriting the derive_less! macro using Rust's procedural macro interface or through a build-script that generates declarative macro code.