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BitLogger/docs/api/file-sink-set-append-mode.md
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---
name: file-sink-set-append-mode
group: api
category: sink
update-time: 20260613
description: Update the append-mode policy used by a FileSink for later reopen behavior.
key-word:
- file
- sink
- append
- public
---
## File-sink-set-append-mode
Update the append-mode policy used by a `FileSink`. This helper changes future reopen behavior on the concrete sink without forcing an immediate reopen.
### Interface
```moonbit
pub fn FileSink::set_append_mode(self : FileSink, append : Bool) -> Unit {
```
#### input
- `self : FileSink` - File sink whose append-mode policy should change.
- `append : Bool` - New append-mode policy.
### Explanation
Detailed rules explaining key parameters and behaviors
- This method updates stored policy only.
- It does not force an immediate reopen.
- The new value affects later reopen behavior.
- The sink path and current rotation policy are left unchanged.
### How to Use
Here are some specific examples provided.
#### When Need To Change Future Reopen Behavior
When direct recovery code should later prefer append mode explicitly:
```moonbit
sink.set_append_mode(true)
```
In this example, later reopen operations use the updated append policy.
#### When Want To Separate Policy Mutation From Reopen Timing
When code should update policy now and reopen later:
```moonbit
sink.set_append_mode(false)
ignore(sink.reopen_with_current_policy())
```
In this example, policy mutation and reopen timing remain separate decisions.
### Error Case
e.g.:
- If callers need an immediate reopen as part of the same operation, one of the reopen helpers should be used afterward.
- This method does not itself prove that the sink is currently available or writable.
### Notes
1. This helper changes stored policy, not live file-handle state by itself.
2. It is useful when direct file-sink recovery logic wants to stage reopen behavior in advance.