BitLogger/docs/api/filter-sink.md

name, group, category, update-time, description, key-word

name	group	category	update-time	description	key-word
filter-sink	api	sink	20260520	Create a sink that forwards only records matching a predicate.	sink filter predicate public

Filter-sink

Create a sink that forwards only records matching a predicate. This helper is the sink-level counterpart to Logger::with_filter(...).

Interface

pub fn[S] filter_sink(sink : S, predicate : (Record) -> Bool) -> FilterSink[S] {

input

• sink : S - Wrapped sink receiving records that pass the predicate.
• predicate : (Record) -> Bool - Filtering function evaluated for each record.

output

• FilterSink[S] - Predicate-filtering sink.

Explanation

Detailed rules explaining key parameters and behaviors

• Only records for which the predicate returns true are forwarded.
• This helper is useful for sink-first composition and explicit routing graphs.
• Use the logger-level helper when the filter should be attached after Logger::new(...) instead.

How to Use

Here are some specific examples provided.

When Need Predicate Filtering At Sink Construction Time

When a sink graph should reject records before they reach the destination:

let sink = filter_sink(console_sink(), fn(rec) {
  rec.target == "kept"
})

In this example, only matching records are forwarded to the wrapped sink.

Error Case

e.g.:

• If record selection should be attached to an already-built logger, use with_filter(...) instead.

• Predicate logic is caller-defined, so accidental over-filtering comes from predicate choice.

Notes

1. This helper is useful for sink-first composition graphs.

2. It works well with predicate builders such as target_is(...) and all_of(...).