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BitLogger/docs/api/runtime-sink-file-set-policy.md
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2026-06-13 23:21:24 +08:00

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---
name: runtime-sink-file-set-policy
group: api
category: runtime
update-time: 20260613
description: Apply a bundled runtime file policy update to a file-backed RuntimeSink.
key-word:
- runtime
- sink
- file
- public
---
## Runtime-sink-file-set-policy
Apply a bundled runtime file policy update to a `RuntimeSink`. This helper updates append mode, auto-flush, and rotation together through one runtime policy object on direct sink values.
### Interface
```moonbit
pub fn RuntimeSink::file_set_policy(self : RuntimeSink, policy : FileSinkPolicy) -> Bool {
```
#### input
- `self : RuntimeSink` - Runtime sink whose file policy should change.
- `policy : FileSinkPolicy` - Bundled runtime file policy to apply.
#### output
- `Bool` - Whether the policy update was applied.
### Explanation
Detailed rules explaining key parameters and behaviors
- Plain `File` runtime variants update append, auto-flush, and rotation together on the wrapped `FileSink` and return `true`.
- `QueuedFile` runtime variants forward the policy update to the wrapped inner `FileSink` and return `true`.
- Non-file runtime variants return `false`.
- This helper is broader than the single-setting setters because it updates the whole file policy in one call.
### How to Use
Here are some specific examples provided.
#### When Need Bundled Runtime Policy Changes
When append, flush, and rotation should change together:
```moonbit
ignore(sink.file_set_policy(FileSinkPolicy::new(
append=true,
auto_flush=false,
rotation=Some(file_rotation(2048, max_backups=2)),
)))
```
In this example, runtime file behavior is updated as one policy change.
#### When Apply A Policy Snapshot
When a previously captured or computed policy should be restored:
```moonbit
let ok = sink.file_set_policy(policy)
```
In this example, callers can reapply a whole policy object without splitting it into separate setter calls.
### Error Case
e.g.:
- If the runtime sink is not file-backed, the method returns `false`.
- If callers only need to change one setting, a narrower setter such as `file_set_auto_flush(...)` or `file_set_rotation(...)` may be clearer.
### Notes
1. Use this helper when the runtime policy should be treated as one cohesive object.
2. It pairs naturally with `file_policy()` and `file_default_policy()`.