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bevy_reflect: Get owned fields (bevyengine#5728)
# Objective Sometimes it's useful to be able to retrieve all the fields of a container type so that they may be processed separately. With reflection, however, we typically only have access to references. The only alternative is to "clone" the value using `Reflect::clone_value`. This, however, returns a Dynamic type in most cases. The solution there would be to use `FromReflect` instead, but this also has a problem in that it means we need to add `FromReflect` as an additional bound. ## Solution Add a `drain` method to all container traits. This returns a `Vec<Box<dyn Reflect>>` (except for `Map` which returns `Vec<(Box<dyn Reflect>, Box<dyn Reflect>)>`). This allows us to do things a lot simpler. For example, if we finished processing a struct and just need a particular value: ```rust // === OLD === // /// May or may not return a Dynamic*** value (even if `container` wasn't a `DynamicStruct`) fn get_output(container: Box<dyn Struct>, output_index: usize) -> Box<dyn Reflect> { container.field_at(output_index).unwrap().clone_value() } // === NEW === // /// Returns _exactly_ whatever was in the given struct fn get_output(container: Box<dyn Struct>, output_index: usize) -> Box<dyn Reflect> { container.drain().remove(output_index).unwrap() } ``` ### Discussion * Is `drain` the best method name? It makes sense that it "drains" all the fields and that it consumes the container in the process, but I'm open to alternatives. --- ## Changelog * Added a `drain` method to the following traits: * `Struct` * `TupleStruct` * `Tuple` * `Array` * `List` * `Map` * `Enum`
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