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77 lines
2.2 KiB
Markdown
77 lines
2.2 KiB
Markdown
---
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name: record-with-message
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group: api
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category: record
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update-time: 20260613
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description: Return a copy of a record with a replaced message field.
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key-word:
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- record
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- message
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- transform
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- public
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---
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## Record-with-message
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Return a copy of a `Record` with a different `message`. This helper is the narrowest way to rewrite the visible event text while preserving the rest of the structured event data.
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### Interface
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```moonbit
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pub fn Record::with_message(self : Record, message : String) -> Record {}
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```
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#### input
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- `self : Record` - Base record whose message should be replaced.
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- `message : String` - New message text for the returned record.
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#### output
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- `Record` - New record value carrying the updated message.
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### Explanation
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Detailed rules explaining key parameters and behaviors
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- This helper returns a new record value instead of mutating the original one.
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- Only the `message` field is replaced.
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- `level`, `timestamp_ms`, `target`, and `fields` are preserved.
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- This is useful for adapters, tests, or explicit value-level rewriting before formatting or sink dispatch.
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### How to Use
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Here are some specific examples provided.
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#### When Need To Rewrite One Event Message
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When one record should keep its metadata but use different visible text:
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```moonbit
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let rec = Record::new(Level::Error, "raw failure", target="bridge")
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let next = rec.with_message("dispatch failed")
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```
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In this example, the new message is applied without rebuilding the rest of the record manually.
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#### When Need To Normalize Message Text In Tests
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When one test record should be adapted to a different wording:
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```moonbit
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let rec = Record::new(Level::Info, "ok").with_message("started")
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```
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In this example, the helper keeps the change focused on one field.
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### Error Case
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e.g.:
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- If `message` is empty, the returned record is still valid and simply carries an empty message string.
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- If the same rewrite should be reusable across many records, `prefix_message(...)` or a custom `RecordPatch` may be a better fit.
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### Notes
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1. Use this helper for one-off value-level message replacement.
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2. Use patch helpers when message rewriting should participate in a reusable logger pipeline.
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