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BitLogger/docs/api/configured-logger-file-append-mode.md
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2026-05-12 14:52:23 +08:00

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---
name: configured-logger-file-append-mode
group: api
category: runtime
update-time: 20260512
description: Read the current append-mode policy used by the configured runtime file sink.
key-word:
- logger
- runtime
- file
- public
---
## Configured-logger-file-append-mode
Read the current append-mode policy used by a `ConfiguredLogger` file sink. This helper exposes whether future reopen behavior is currently append-oriented.
### Interface
```moonbit
pub fn ConfiguredLogger::file_append_mode(self : ConfiguredLogger) -> Bool {}
```
#### input
- `self : ConfiguredLogger` - Config-driven runtime logger whose append-mode policy should be inspected.
#### output
- `Bool` - Current append-mode policy for the file sink.
### Explanation
Detailed rules explaining key parameters and behaviors
- File-backed sinks report their current append policy.
- Queued file sinks forward the policy from the wrapped file sink.
- Non-file sinks return `false`.
- This helper reports runtime file policy, not whether a file is currently writable.
### How to Use
Here are some specific examples provided.
#### When Need Runtime Append-policy Visibility
When diagnostics should show how future reopen behavior is configured:
```moonbit
let append = logger.file_append_mode()
```
In this example, the configured logger exposes current reopen policy directly.
#### When Validate Runtime Policy Changes
When policy mutation should be observable after a setter call:
```moonbit
ignore(logger.file_set_append_mode(true))
ignore(logger.file_append_mode())
```
In this example, callers verify the updated append-mode policy.
### Error Case
e.g.:
- If the configured sink is not file-backed, the method returns `false`.
- If callers need the full current file policy rather than just append mode, `file_policy()` is the better API.
### Notes
1. Use this helper when append policy is the only file setting you need to inspect.
2. Pair it with reopen helpers when debugging runtime file behavior.