BitLogger/docs/extend/composition.md

Sink Composition

Presets cover common console and file configurations. Build a Logger::new(...) directly when records need routing or multiple outputs.

Send A Record To Two Destinations

let logger = @log.Logger::new(
  @log.fanout_sink(@log.console_sink(), @log.json_console_sink()),
  min_level=@log.Level::Info,
  target="service",
)

logger.info("request complete", fields=[@log.field("status", "200")])

fanout_sink(...) writes the same record to every child sink. This keeps human-oriented terminal output and machine-oriented JSON output in one application path.

Route Warnings Separately

let logger = @log.Logger::new(
  @log.split_by_level(
    @log.callback_sink(fn(rec) {
      println("alert: \{rec.message}")
    }),
    @log.console_sink(),
    min_level=@log.Level::Warn,
  ),
  min_level=@log.Level::Trace,
  target="service",
)

Use direct sink composition only when the routing behavior is part of the application design. A preset remains easier to audit when one sink is sufficient.

API Reference

• Logger::new(...)
• fanout_sink(...)
• split_by_level(...)
• callback_sink(...)