c0a93aa7a4
# Objective > System chaining is a confusing name: it implies the ability to construct non-linear graphs, and suggests a sense of system ordering that is only incidentally true. Instead, it actually works by passing data from one system to the next, much like the pipe operator. > In the accepted [stageless RFC](https://github.com/bevyengine/rfcs/blob/main/rfcs/45-stageless.md), this concept is renamed to piping, and "system chaining" is used to construct groups of systems with ordering dependencies between them. Fixes #6225. ## Changelog System chaining has been renamed to system piping to improve clarity (and free up the name for new ordering APIs). ## Migration Guide The `.chain(handler_system)` method on systems is now `.pipe(handler_system)`. The `IntoChainSystem` trait is now `IntoPipeSystem`, and the `ChainSystem` struct is now `PipeSystem`.
31 lines
1020 B
Rust
31 lines
1020 B
Rust
//! Illustrates how to make a single system from multiple functions running in sequence,
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//! passing the output of the first into the input of the next.
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use anyhow::Result;
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use bevy::prelude::*;
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fn main() {
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App::new()
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.insert_resource(Message("42".to_string()))
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.add_system(parse_message_system.pipe(handler_system))
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.run();
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}
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#[derive(Resource, Deref)]
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struct Message(String);
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// this system produces a Result<usize> output by trying to parse the Message resource
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fn parse_message_system(message: Res<Message>) -> Result<usize> {
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Ok(message.parse::<usize>()?)
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}
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// This system takes a Result<usize> input and either prints the parsed value or the error message
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// Try changing the Message resource to something that isn't an integer. You should see the error
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// message printed.
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fn handler_system(In(result): In<Result<usize>>) {
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match result {
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Ok(value) => println!("parsed message: {}", value),
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Err(err) => println!("encountered an error: {:?}", err),
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}
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}
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