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Document what Config is and how to use it. (#2185)

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While trying to figure out how to implement a `SystemParam`, I spent a
long time looking for a feature that would do exactly what `Config`
does.  I ignored it at first because all the examples I could find used
`()` and I couldn't see a way to modify it.

This is documented in other places, but `Config` is a logical place to
include some breadcrumbs.  I've added some text that gives a brief
overview of what `Config` is for, and links to the existing docs on
`FunctionSystem::config` for more details.

This would have saved me from embarrassing myself by filing https://github.com/bevyengine/bevy/issues/2178.

Co-authored-by: Carter Anderson <mcanders1@gmail.com>
This commit is contained in:
Daniel Burrows 2021-05-18 00:10:18 +00:00
parent 1f0988be87
commit d4ffa3f490
1 changed files with 12 additions and 0 deletions
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crates/bevy_ecs/src/system/system_param.rs
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@ -49,6 +49,18 @@ pub trait SystemParam: Sized {
/// Additionally, it is the implementor's responsibility to ensure there is no
/// conflicting access across all SystemParams.
pub unsafe trait SystemParamState: Send + Sync + 'static {
/// Values of this type can be used to adjust the behavior of the
/// system parameter. For instance, this can be used to pass
/// values from a `Plugin` to a `System`, or to control the
/// behavior of the `System`.
///
/// The default configuration of the parameter is set by
/// [`SystemParamState::default_config`]. To change it, invoke
/// [`FunctionSystem::config`](super::FunctionSystem::config) when
/// creating the system.
///
/// See [`FunctionSystem::config`](super::FunctionSystem::config)
/// for more information and examples.
type Config: Send + Sync;
fn init(world: &mut World, system_state: &mut SystemState, config: Self::Config) -> Self;
#[inline]