Formatted-callback-sink

Create a callback sink from a RecordFormatter and a string callback. This is the low-level text-delivery constructor for integrations that already have custom record-to-string formatting logic and want the final rendered text in a callback.

Interface

pub fn formatted_callback_sink(
  formatter : RecordFormatter,
  callback : (String) -> Unit,
) -> FormattedCallbackSink {

input

• formatter : RecordFormatter - Function used to render each record into a final string.
• callback : (String) -> Unit - Function receiving the rendered string.

output

• FormattedCallbackSink - Callback sink that forwards formatter output as text.

Explanation

Detailed rules explaining key parameters and behaviors

• This helper stores both the provided formatter and callback directly inside the sink.
• The callback receives exactly the string returned by the formatter.
• It is lower-level than text_callback_sink(...) because it works with arbitrary RecordFormatter functions instead of TextFormatter values.
• Use it when formatting logic is already expressed as code rather than formatter configuration data.

How to Use

Here are some specific examples provided.

When Need Custom Rendered Text In A Callback Integration

When an adapter should receive a hand-formatted line instead of a structured record:

let formatter : RecordFormatter = fn(rec) { "[" + rec.level.label() + "] " + rec.message }
let sink = formatted_callback_sink(formatter, fn(line) { println(line) })

In this example, the callback receives exactly the custom rendered text.

When Already Working With Shared RecordFormatter Values

When formatter creation already happened elsewhere and should be reused directly:

fn make_sink(formatter : RecordFormatter) -> FormattedCallbackSink {
  formatted_callback_sink(formatter, fn(line) { println(line) })
}

In this example, the low-level sink constructor keeps the integration in terms of formatter functions and final text callbacks.

Error Case

e.g.:

• If structured field access is required inside the callback, callback_sink(...) is the better API because it forwards full Record values.

• If a configurable text formatting policy is preferred over a code-defined function, text_callback_sink(...) is usually the better API.

Notes

1. Use this helper when the formatter is already a RecordFormatter and the destination expects final text.

2. Use text_callback_sink(...) when the source formatting policy is a TextFormatter value.