pipe_io/
stage.rs

1//! The [`Stage`] trait.
2//!
3//! Stages receive items one at a time and emit zero or more outputs via
4//! an [`Emit`] handle. The closure-based adapters (`map`, `filter`, ...)
5//! are exposed as methods on [`crate::PipelineBuilder`].
6
7use crate::emit::Emit;
8use crate::error::StageError;
9
10/// Transform stage in a pipeline.
11///
12/// Stages emit zero or more outputs per input via the `out` handle.
13/// 1:1 maps emit once per input, filters emit 0..1 per input,
14/// batching/windowing emit 0+ per input and additionally use
15/// [`Stage::flush`] to emit a final partial group at end-of-stream.
16pub trait Stage {
17    /// Type of item this stage consumes.
18    type Input;
19    /// Type of item this stage emits.
20    type Output;
21    /// Error type the stage can produce.
22    type Error: StageError;
23
24    /// Process a single input item.
25    ///
26    /// # Errors
27    ///
28    /// Returns `Err(Self::Error)` on stage failure. The driver wraps
29    /// this in [`crate::Error::Stage`].
30    fn process(
31        &mut self,
32        item: Self::Input,
33        out: &mut dyn Emit<Item = Self::Output>,
34    ) -> Result<(), Self::Error>;
35
36    /// Emit any buffered output at end-of-stream.
37    ///
38    /// Default impl does nothing.
39    ///
40    /// # Errors
41    ///
42    /// Returns `Err(Self::Error)` on stage failure.
43    fn flush(&mut self, _out: &mut dyn Emit<Item = Self::Output>) -> Result<(), Self::Error> {
44        Ok(())
45    }
46}
pipe_io/stage.rs

pipe_io/
stage.rs
