CODEWITHSUNDEEP
rustenums
mye
mye

Reputation: 103

Create macro to simplify declaration of deeply nested enum?

I want to use deeply nested enums to represent blocks in my game:

enum Element { Void, Materal(Material) }
enum Material { Gas(Gas), NonGas(NonGas) }
enum NonGas { Liquid(Liquid), Solid(Solid) }
enum Solid { MovableSolid(MovableSolid), ImmovableSolid(ImmovableSolid) }
enum Gas { Smoke }
enum Liquid { Water }
enum ImmovableSolid { Bedrock }
enum MovableSolid { Sand, GunPowder }

I found it very verbose to declare an Element:

let block: Element = Element::Materal(Material::NonGas(NonGas::Solid(Solid::ImmovableSolid(ImmovableSolid::Bedrock))));

Is it possible to create a macro to add syntactic sugar for my enum declaration?

I'm hoping to create a macro that can automagically resolve the enum path, for example

let block: Element = NewElement!(ImmovableSolid::Bedrock);

Upvotes: 0

Views: 101

Answers (1)

Jeremy Meadows
Jeremy Meadows

Reputation: 2581

Using cdhowie's From idea, I think you'd only need trait impls from your lowest level enums. You can skip ones like impl From<Material> for Element because you need a child to create a Material, so it doesn't really make sense to start at that level.

impl From<Gas> for Element {
    fn from(e: Gas) -> Element {
        Element::Materal(Material::Gas(e))
    }
}

impl From<Liquid> for Element {
    fn from(e: Liquid) -> Element {
        Element::Materal(Material::NonGas(NonGas::Liquid(e)))
    }
}

impl From<ImmovableSolid> for Element {
    fn from(e: ImmovableSolid) -> Element {
        Element::Materal(Material::NonGas(NonGas::Solid(Solid::ImmovableSolid(e))))
    }
}

impl From<MovableSolid> for Element {
    fn from(e: MovableSolid) -> Element {
        Element::Materal(Material::NonGas(NonGas::Solid(Solid::MovableSolid(e))))
    }
}

fn main() {
    println!("{:?}", Element::from(ImmovableSolid::Bedrock));
}

Upvotes: 2

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