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use super::stateless_op::StatelessOp;
use crate::channels::operator_io::Output;
use crate::stream::StreamBuilder;
use crate::types::{Data, DataMessage, MaybeKey};
use crate::types::{Message, Timestamp};
/// Filter messages in a stream
pub trait Filter<K, V, T>: super::sealed::Sealed {
/// Filters the datastream based on a given predicate.
///
/// The given function receives an immutable reference to the value
/// of every data message reaching this operator.
/// If the function returns `true`, the message will be retained and
/// passed downstream, if the function returns `false`, the message
/// will be discarded.
///
/// # Example
///
/// Only retain numbers <= 42
/// ```rust
/// use malstrom::operators::*;
/// use malstrom::runtime::SingleThreadRuntime;
/// use malstrom::snapshot::NoPersistence;
/// use malstrom::sources::{SingleIteratorSource, StatelessSource};
/// use malstrom::worker::StreamProvider;
/// use malstrom::sinks::{VecSink, StatelessSink};
///
/// let sink = VecSink::new();
/// let sink_clone = sink.clone();
///
/// SingleThreadRuntime::builder()
/// .persistence(NoPersistence)
/// .build(move |provider: &mut dyn StreamProvider| {
/// provider.new_stream()
/// .source("numbers", StatelessSource::new(SingleIteratorSource::new(0..100)))
/// .filter("filter", |x| *x <= 42)
/// .sink("sink", StatelessSink::new(sink_clone));
/// })
/// .execute()
/// .unwrap();
/// let expected: Vec<i32> = (0..=42).collect();
/// let out: Vec<i32> = sink.into_iter().map(|x| x.value).collect();
/// assert_eq!(out, expected);
/// ```
fn filter(self, name: &str, filter: impl FnMut(&V) -> bool + 'static)
-> StreamBuilder<K, V, T>;
}
impl<K, V, T> Filter<K, V, T> for StreamBuilder<K, V, T>
where
K: MaybeKey,
V: Data,
T: Timestamp,
{
fn filter(
self,
name: &str,
mut filter: impl FnMut(&V) -> bool + 'static,
) -> StreamBuilder<K, V, T> {
self.stateless_op(
name,
move |item: DataMessage<K, V, T>, out: &mut Output<K, V, T>| {
if filter(&item.value) {
out.send(Message::Data(item))
}
},
)
}
}
#[cfg(test)]
mod tests {
use crate::{
operators::*,
sinks::StatelessSink,
sources::{SingleIteratorSource, StatelessSource},
testing::{get_test_rt, VecSink},
};
#[test]
fn test_filter() {
let collector = VecSink::new();
let rt = get_test_rt(|provider| {
provider
.new_stream()
.source(
"source",
StatelessSource::new(SingleIteratorSource::new(0..100)),
)
.filter("less-than-42", |x| *x < 42)
.sink("sink", StatelessSink::new(collector.clone()));
});
rt.execute().unwrap();
let collected: Vec<usize> = collector.into_iter().map(|x| x.value).collect();
let expected: Vec<usize> = (0..42).collect();
assert_eq!(expected, collected)
}
}