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use crate::system::{IntoSystem, System};
use std::borrow::Cow;
use super::{CombinatorSystem, Combine};
/// A [`System`] created by piping the output of the first system into the input of the second.
///
/// This can be repeated indefinitely, but system pipes cannot branch: the output is consumed by the receiving system.
///
/// Given two systems `A` and `B`, A may be piped into `B` as `A.pipe(B)` if the output type of `A` is
/// equal to the input type of `B`.
///
/// Note that for [`FunctionSystem`](crate::system::FunctionSystem)s the output is the return value
/// of the function and the input is the first [`SystemParam`](crate::system::SystemParam) if it is
/// tagged with [`In`](crate::system::In) or `()` if the function has no designated input parameter.
///
/// # Examples
///
/// ```
/// use std::num::ParseIntError;
///
/// use bevy_ecs::prelude::*;
///
/// fn main() {
/// let mut world = World::default();
/// world.insert_resource(Message("42".to_string()));
///
/// // pipe the `parse_message_system`'s output into the `filter_system`s input
/// let mut piped_system = parse_message_system.pipe(filter_system);
/// piped_system.initialize(&mut world);
/// assert_eq!(piped_system.run((), &mut world), Some(42));
/// }
///
/// #[derive(Resource)]
/// struct Message(String);
///
/// fn parse_message_system(message: Res<Message>) -> Result<usize, ParseIntError> {
/// message.0.parse::<usize>()
/// }
///
/// fn filter_system(In(result): In<Result<usize, ParseIntError>>) -> Option<usize> {
/// result.ok().filter(|&n| n < 100)
/// }
/// ```
pub type PipeSystem<SystemA, SystemB> = CombinatorSystem<Pipe, SystemA, SystemB>;
#[doc(hidden)]
pub struct Pipe;
impl<A, B> Combine<A, B> for Pipe
where
A: System,
B: System<In = A::Out>,
{
type In = A::In;
type Out = B::Out;
fn combine(
input: Self::In,
a: impl FnOnce(<A as System>::In) -> <A as System>::Out,
b: impl FnOnce(<B as System>::In) -> <B as System>::Out,
) -> Self::Out {
let value = a(input);
b(value)
}
}
/// An extension trait providing the [`IntoPipeSystem::pipe`] method to pass input from one system into the next.
///
/// The first system must have return type `T`
/// and the second system must have [`In<T>`](crate::system::In) as its first system parameter.
///
/// This trait is blanket implemented for all system pairs that fulfill the type requirements.
///
/// See [`PipeSystem`].
pub trait IntoPipeSystem<ParamA, Payload, SystemB, ParamB, Out>:
IntoSystem<(), Payload, ParamA> + Sized
where
SystemB: IntoSystem<Payload, Out, ParamB>,
{
/// Pass the output of this system `A` into a second system `B`, creating a new compound system.
fn pipe(self, system: SystemB) -> PipeSystem<Self::System, SystemB::System>;
}
impl<SystemA, ParamA, Payload, SystemB, ParamB, Out>
IntoPipeSystem<ParamA, Payload, SystemB, ParamB, Out> for SystemA
where
SystemA: IntoSystem<(), Payload, ParamA>,
SystemB: IntoSystem<Payload, Out, ParamB>,
{
fn pipe(self, system: SystemB) -> PipeSystem<SystemA::System, SystemB::System> {
let system_a = IntoSystem::into_system(self);
let system_b = IntoSystem::into_system(system);
let name = format!("Pipe({}, {})", system_a.name(), system_b.name());
PipeSystem::new(system_a, system_b, Cow::Owned(name))
}
}
/// A collection of common adapters for [piping](super::PipeSystem) the result of a system.
pub mod adapter {
use crate::system::In;
use bevy_utils::tracing;
use std::fmt::Debug;
/// Converts a regular function into a system adapter.
///
/// # Examples
/// ```
/// use bevy_ecs::prelude::*;
///
/// fn return1() -> u64 { 1 }
///
/// return1
/// .pipe(system_adapter::new(u32::try_from))
/// .pipe(system_adapter::unwrap)
/// .pipe(print);
///
/// fn print(In(x): In<impl std::fmt::Debug>) {
/// println!("{x:?}");
/// }
/// ```
pub fn new<T, U>(mut f: impl FnMut(T) -> U) -> impl FnMut(In<T>) -> U {
move |In(x)| f(x)
}
/// System adapter that unwraps the `Ok` variant of a [`Result`].
/// This is useful for fallible systems that should panic in the case of an error.
///
/// There is no equivalent adapter for [`Option`]. Instead, it's best to provide
/// an error message and convert to a `Result` using `ok_or{_else}`.
///
/// # Examples
///
/// Panicking on error
///
/// ```
/// use bevy_ecs::prelude::*;
///
/// // Building a new schedule/app...
/// let mut sched = Schedule::default();
/// sched.add_system(
/// // Panic if the load system returns an error.
/// load_save_system.pipe(system_adapter::unwrap)
/// )
/// // ...
/// # ;
/// # let mut world = World::new();
/// # sched.run(&mut world);
///
/// // A system which may fail irreparably.
/// fn load_save_system() -> Result<(), std::io::Error> {
/// let save_file = open_file("my_save.json")?;
/// dbg!(save_file);
/// Ok(())
/// }
/// # fn open_file(name: &str) -> Result<&'static str, std::io::Error>
/// # { Ok("hello world") }
/// ```
pub fn unwrap<T, E: Debug>(In(res): In<Result<T, E>>) -> T {
res.unwrap()
}
/// System adapter that utilizes the [`bevy_utils::tracing::info!`] macro to print system information.
///
/// # Examples
///
/// ```
/// use bevy_ecs::prelude::*;
///
/// // Building a new schedule/app...
/// let mut sched = Schedule::default();
/// sched.add_system(
/// // Prints system information.
/// data_pipe_system.pipe(system_adapter::info)
/// )
/// // ...
/// # ;
/// # let mut world = World::new();
/// # sched.run(&mut world);
///
/// // A system that returns a String output.
/// fn data_pipe_system() -> String {
/// "42".to_string()
/// }
/// ```
pub fn info<T: Debug>(In(data): In<T>) {
tracing::info!("{:?}", data);
}
/// System adapter that utilizes the [`bevy_utils::tracing::debug!`] macro to print the output of a system.
///
/// # Examples
///
/// ```
/// use bevy_ecs::prelude::*;
///
/// // Building a new schedule/app...
/// let mut sched = Schedule::default();
/// sched.add_system(
/// // Prints debug data from system.
/// parse_message_system.pipe(system_adapter::dbg)
/// )
/// // ...
/// # ;
/// # let mut world = World::new();
/// # sched.run(&mut world);
///
/// // A system that returns a Result<usize, String> output.
/// fn parse_message_system() -> Result<usize, std::num::ParseIntError> {
/// Ok("42".parse()?)
/// }
/// ```
pub fn dbg<T: Debug>(In(data): In<T>) {
tracing::debug!("{:?}", data);
}
/// System adapter that utilizes the [`bevy_utils::tracing::warn!`] macro to print the output of a system.
///
/// # Examples
///
/// ```
/// use bevy_ecs::prelude::*;
///
/// // Building a new schedule/app...
/// # let mut sched = Schedule::default();
/// sched.add_system(
/// // Prints system warning if system returns an error.
/// warning_pipe_system.pipe(system_adapter::warn)
/// )
/// // ...
/// # ;
/// # let mut world = World::new();
/// # sched.run(&mut world);
///
/// // A system that returns a Result<(), String> output.
/// fn warning_pipe_system() -> Result<(), String> {
/// Err("Got to rusty?".to_string())
/// }
/// ```
pub fn warn<E: Debug>(In(res): In<Result<(), E>>) {
if let Err(warn) = res {
tracing::warn!("{:?}", warn);
}
}
/// System adapter that utilizes the [`bevy_utils::tracing::error!`] macro to print the output of a system.
///
/// # Examples
///
/// ```
/// use bevy_ecs::prelude::*;
/// // Building a new schedule/app...
/// let mut sched = Schedule::default();
/// sched.add_system(
/// // Prints system error if system fails.
/// parse_error_message_system.pipe(system_adapter::error)
/// )
/// // ...
/// # ;
/// # let mut world = World::new();
/// # sched.run(&mut world);
///
/// // A system that returns a Result<())> output.
/// fn parse_error_message_system() -> Result<(), String> {
/// Err("Some error".to_owned())
/// }
/// ```
pub fn error<E: Debug>(In(res): In<Result<(), E>>) {
if let Err(error) = res {
tracing::error!("{:?}", error);
}
}
/// System adapter that ignores the output of the previous system in a pipe.
/// This is useful for fallible systems that should simply return early in case of an `Err`/`None`.
///
/// # Examples
///
/// Returning early
///
/// ```
/// use bevy_ecs::prelude::*;
///
/// // Marker component for an enemy entity.
/// #[derive(Component)]
/// struct Monster;
///
/// // Building a new schedule/app...
/// # let mut sched = Schedule::default(); sched
/// .add_system(
/// // If the system fails, just move on and try again next frame.
/// fallible_system.pipe(system_adapter::ignore)
/// )
/// // ...
/// # ;
/// # let mut world = World::new();
/// # sched.run(&mut world);
///
/// // A system which may return early. It's more convenient to use the `?` operator for this.
/// fn fallible_system(
/// q: Query<Entity, With<Monster>>
/// ) -> Option<()> {
/// let monster_id = q.iter().next()?;
/// println!("Monster entity is {monster_id:?}");
/// Some(())
/// }
/// ```
pub fn ignore<T>(In(_): In<T>) {}
#[cfg(test)]
#[test]
fn assert_systems() {
use std::str::FromStr;
use crate::{prelude::*, system::assert_is_system};
/// Mocks a system that returns a value of type `T`.
fn returning<T>() -> T {
unimplemented!()
}
/// Mocks an exclusive system that takes an input and returns an output.
fn exclusive_in_out<A, B>(_: In<A>, _: &mut World) -> B {
unimplemented!()
}
fn not(In(val): In<bool>) -> bool {
!val
}
assert_is_system(returning::<Result<u32, std::io::Error>>.pipe(unwrap));
assert_is_system(returning::<Option<()>>.pipe(ignore));
assert_is_system(returning::<&str>.pipe(new(u64::from_str)).pipe(unwrap));
assert_is_system(exclusive_in_out::<(), Result<(), std::io::Error>>.pipe(error));
assert_is_system(returning::<bool>.pipe(exclusive_in_out::<bool, ()>));
returning::<()>.run_if(returning::<bool>.pipe(not));
}
}