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# Objective Any time we wish to transform the output of a system, we currently use system piping to do so: ```rust my_system.pipe(|In(x)| do_something(x)) ``` Unfortunately, system piping is not a zero cost abstraction. Each call to `.pipe` requires allocating two extra access sets: one for the second system and one for the combined accesses of both systems. This also adds extra work to each call to `update_archetype_component_access`, which stacks as one adds multiple layers of system piping. ## Solution Add the `AdapterSystem` abstraction: similar to `CombinatorSystem`, this allows you to implement a trait to generically control how a system is run and how its inputs and outputs are processed. Unlike `CombinatorSystem`, this does not have any overhead when computing world accesses which makes it ideal for simple operations such as inverting or ignoring the output of a system. Add the extension method `.map(...)`: this is similar to `.pipe(...)`, only it accepts a closure as an argument instead of an `In<T>` system. ```rust my_system.map(do_something) ``` This has the added benefit of making system names less messy: a system that ignores its output will just be called `my_system`, instead of `Pipe(my_system, ignore)` --- ## Changelog TODO ## Migration Guide The `system_adapter` functions have been deprecated: use `.map` instead, which is a lightweight alternative to `.pipe`. ```rust // Before: my_system.pipe(system_adapter::ignore) my_system.pipe(system_adapter::unwrap) my_system.pipe(system_adapter::new(T::from)) // After: my_system.map(std::mem::drop) my_system.map(Result::unwrap) my_system.map(T::from) // Before: my_system.pipe(system_adapter::info) my_system.pipe(system_adapter::dbg) my_system.pipe(system_adapter::warn) my_system.pipe(system_adapter::error) // After: my_system.map(bevy_utils::info) my_system.map(bevy_utils::dbg) my_system.map(bevy_utils::warn) my_system.map(bevy_utils::error) ``` --------- Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com> |
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