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Nanaloveyuki
82 lines
2.8 KiB
Markdown
82 lines
2.8 KiB
Markdown
---
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name: formatted-callback-sink
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group: api
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category: sink
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update-time: 20260613
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description: Create a callback sink from a low-level RecordFormatter function and string callback.
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key-word:
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- sink
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- callback
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- formatter
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- public
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---
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## Formatted-callback-sink
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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.
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### Interface
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```moonbit
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pub fn formatted_callback_sink(
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formatter : RecordFormatter,
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callback : (String) -> Unit,
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) -> FormattedCallbackSink {
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```
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#### input
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- `formatter : RecordFormatter` - Function used to render each record into a final string.
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- `callback : (String) -> Unit` - Function receiving the rendered string.
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#### output
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- `FormattedCallbackSink` - Callback sink that forwards formatter output as text.
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### Explanation
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Detailed rules explaining key parameters and behaviors
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- This helper stores both the provided formatter and callback directly inside the sink.
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- The callback receives exactly the string returned by the formatter.
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- It is lower-level than `text_callback_sink(...)` because it works with arbitrary `RecordFormatter` functions instead of `TextFormatter` values.
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- Use it when formatting logic is already expressed as code rather than formatter configuration data.
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### How to Use
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Here are some specific examples provided.
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#### When Need Custom Rendered Text In A Callback Integration
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When an adapter should receive a hand-formatted line instead of a structured record:
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```moonbit
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let formatter : RecordFormatter = fn(rec) { "[" + rec.level.label() + "] " + rec.message }
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let sink = formatted_callback_sink(formatter, fn(line) { println(line) })
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```
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In this example, the callback receives exactly the custom rendered text.
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#### When Already Working With Shared RecordFormatter Values
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When formatter creation already happened elsewhere and should be reused directly:
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```moonbit
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fn make_sink(formatter : RecordFormatter) -> FormattedCallbackSink {
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formatted_callback_sink(formatter, fn(line) { println(line) })
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}
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```
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In this example, the low-level sink constructor keeps the integration in terms of formatter functions and final text callbacks.
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### Error Case
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e.g.:
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- If structured field access is required inside the callback, `callback_sink(...)` is the better API because it forwards full `Record` values.
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- If a configurable text formatting policy is preferred over a code-defined function, `text_callback_sink(...)` is usually the better API.
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### Notes
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1. Use this helper when the formatter is already a `RecordFormatter` and the destination expects final text.
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2. Use `text_callback_sink(...)` when the source formatting policy is a `TextFormatter` value.
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