subenum

Subenum is a simple proc-macro to derive subsets of enums. It allows conversion between the parent and the child, will derive any traits on the child that you have on the parent, and will implement PartialEq between the parent and child if you derive it on the parent.

Simple Example

I think the simplest way to explain it is with an example:

use subenum::subenum;

#[subenum(Edible)]
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub enum Plant {
    #[subenum(Edible)]
    Basil,
    #[subenum(Edible)]
    Tomato,
    Manzanita,
    Pine,
}

fn main() -> Result<(), EdibleConvertError> {
    let plant = Plant::Tomato;

    // We can convert between them.
    let edible = Edible::try_from(plant)?;
    let _plant2 = Plant::from(edible);

    // We can compare them.
    assert_eq!(plant, edible);

    // We derive anything that's derived on the parent, such as clone.
    let edible2 = edible.clone();

    Ok(())
}

Complex Example

In addition to simple enums and built-in traits, subenum works with complex enums and third-party attributes.

use subenum::subenum;

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum AppleType {
    CosmicCrisp,
    Fuji,
    PinkLady,
}

#[subenum(Foo, Tree, Edible, Grass)]
#[derive(Debug, Clone, Copy, PartialEq, strum::Display)]
pub enum Plant<'a, T> {
    #[subenum(Foo)]
    #[strum(serialize = "This is not a plant!")]
    Foo { x: i32, y: i32 },
    #[subenum(Tree, Edible)]
    Apple(AppleType),
    #[subenum(Grass)]
    Bamboo(&'a str),
    #[subenum(Edible)]
    Basil(T),
    #[subenum(Tree)]
    Fir,
    #[subenum(Tree)]
    Pine,
    #[subenum(Edible)]
    Tomato,
    #[subenum(Edible, Grass)]
    Wheat,
}

fn main() -> Result<(), TreeConvertError> {
    let plant: Plant<'_, u32> = Plant::Apple(AppleType::CosmicCrisp);
    let tree = Tree::try_from(plant)?;

    assert_eq!(plant, tree);

    let tree2 = tree.clone();
    assert_eq!(tree2.to_string(), "Apple");

    let foo = Foo::Foo { x: 3, y: 4 };
    assert_eq!(foo.to_string(), "This is not a plant!");

    let edible = Edible::Basil(3);
    let plant = Plant::from(edible);

    assert_eq!(plant.to_string(), "Basil");

    // Can't compare two subenums.
    // assert_ne!(tree2, edible);

    // But we can do some conversion-trickery
    assert_ne!(Plant::from(tree2), Plant::from(edible));

    Ok(())
}

Subenum-specific proc-macros

Maybe you have an enum that can't be Copyd, but the subenum can, and you want to derive it:

use subenum::subenum;

#[subenum(Bar, Qux(derive(Copy)))]
#[derive(Debug, PartialEq, Eq, Clone)]
pub enum Foo {
    #[subenum(Bar)]
    A(String),
    #[subenum(Qux)]
    B,
    #[subenum(Bar, Qux)]
    C(u8),
}

fn main() {
    let b = Qux::B;
    let c = b;
    assert_eq!(b, c);
}

Limitations

Bound lifetimes (e.g. for<'a, 'b, 'c>) are not currently supported. Please open a ticket if these are desired.

Features

• default - std and error_trait
• std - Use standard library collections and allocators within this proc macro
• error_trait - Implement Error for ConvertError types.
  • When combined with nightly and #![feature(error_in_core)] supports #[no_std]
  • Otherwise, this feature requires std as well.