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Merged
alice-i-cecile merged 5 commits into from
Mar 21, 2025
Merged

Required components accept const values (#16720) #18309

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2d06361
first draft: require enums with =
Wuketuke Mar 14, 2025
caa463d
made doc tests pass
Wuketuke Mar 14, 2025
95aa6cf
simplified that code
Wuketuke Mar 14, 2025
0a8421a
updated docs to show that const values are valid too
Wuketuke Mar 14, 2025
2ab9c58
Clearer docs on abbreviated constants
alice-i-cecile Mar 20, 2025
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6 changes: 6 additions & 0 deletions crates/bevy_ecs/macros/src/component.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -611,6 +611,12 @@ impl Parse for Require {
let func = content.parse::<Path>()?;
Some(RequireFunc::Path(func))
}
} else if input.peek(Token![=]) {
let _t: syn::Token![=] = input.parse()?;
let label: Ident = input.parse()?;
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@Brezak Brezak Mar 14, 2025

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We could parse out an expression instead and support more ways to set the value.

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@Wuketuke Wuketuke Mar 14, 2025

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yes, but you would somehow need to extract the type from the expression, so it will be messy

let tokens: TokenStream = quote::quote! (|| #path::#label).into();
let func = syn::parse(tokens).unwrap();
Some(RequireFunc::Closure(func))
} else {
None
};
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32 changes: 32 additions & 0 deletions crates/bevy_ecs/src/component.rs
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Expand Up @@ -180,11 +180,43 @@ use thiserror::Error;
/// }
///
/// # let mut world = World::default();
/// // This will implicitly also insert C with the init_c() constructor
/// let id = world.spawn(A).id();
/// assert_eq!(&C(10), world.entity(id).get::<C>().unwrap());
///
/// // This will implicitly also insert C with the `|| C(20)` constructor closure
/// let id = world.spawn(B).id();
/// assert_eq!(&C(20), world.entity(id).get::<C>().unwrap());
/// ```
///
/// For convenience sake, you can abbreviate enum labels or constant values, with the type inferred to match that of the component you are requiring:
///
/// ```
/// # use bevy_ecs::prelude::*;
/// #[derive(Component)]
/// #[require(B = One, C = ONE)]
/// struct A;
///
/// #[derive(Component, PartialEq, Eq, Debug)]
/// enum B {
/// Zero,
/// One,
/// Two
/// }
///
/// #[derive(Component, PartialEq, Eq, Debug)]
/// struct C(u8);
///
/// impl C {
/// pub const ONE: Self = Self(1);
/// }
///
/// # let mut world = World::default();
/// let id = world.spawn(A).id();
/// assert_eq!(&B::One, world.entity(id).get::<B>().unwrap());
/// assert_eq!(&C(1), world.entity(id).get::<C>().unwrap());
/// ````
///
/// Required components are _recursive_. This means, if a Required Component has required components,
/// those components will _also_ be inserted if they are missing:
///
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