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# Objective Requires are currently more verbose than they need to be. People would like to define inline component values. Additionally, the current `#[require(Foo(custom_constructor))]` and `#[require(Foo(|| Foo(10))]` syntax doesn't really make sense within the context of the Rust type system. #18309 was an attempt to improve ergonomics for some cases, but it came at the cost of even more weirdness / unintuitive behavior. Our approach as a whole needs a rethink. ## Solution Rework the `#[require()]` syntax to make more sense. This is a breaking change, but I think it will make the system easier to learn, while also improving ergonomics substantially: ```rust #[derive(Component)] #[require( A, // this will use A::default() B(1), // inline tuple-struct value C { value: 1 }, // inline named-struct value D::Variant, // inline enum variant E::SOME_CONST, // inline associated const F::new(1), // inline constructor G = returns_g(), // an expression that returns G H = SomethingElse::new(), // expression returns SomethingElse, where SomethingElse: Into<H> )] struct Foo; ``` ## Migration Guide Custom-constructor requires should use the new expression-style syntax: ```rust // before #[derive(Component)] #[require(A(returns_a))] struct Foo; // after #[derive(Component)] #[require(A = returns_a())] struct Foo; ``` Inline-closure-constructor requires should use the inline value syntax where possible: ```rust // before #[derive(Component)] #[require(A(|| A(10))] struct Foo; // after #[derive(Component)] #[require(A(10)] struct Foo; ``` In cases where that is not possible, use the expression-style syntax: ```rust // before #[derive(Component)] #[require(A(|| A(10))] struct Foo; // after #[derive(Component)] #[require(A = A(10)] struct Foo; ``` --------- Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com> Co-authored-by: François Mockers <mockersf@gmail.com> |
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