📝 document file sink policy state methods

2026-07-31 07:24:31 +00:00 · 2026-06-13 22:23:35 +08:00
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+---
+name: file-sink-policy-matches-default
+group: api
+category: sink
+update-time: 20260613
+description: Read whether the current FileSink policy still matches its default policy.
+key-word:
+    - file
+    - sink
+    - policy
+    - public
+---
+
+## File-sink-policy-matches-default
+
+Read whether the current runtime file policy of a `FileSink` still matches its default policy. This helper is useful for detecting direct policy drift on the sink.
+
+### Interface
+
+```moonbit
+pub fn FileSink::policy_matches_default(self : FileSink) -> Bool {
+```
+
+#### input
+
+- `self : FileSink` - File sink whose runtime policy drift should be checked.
+
+#### output
+
+- `Bool` - Whether the current runtime file policy still matches the default.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- The method compares current append and auto-flush settings directly.
+- Rotation drift is checked structurally, comparing `max_bytes` and `max_backups` when both sides are present.
+- This helper is a compact drift signal when callers do not need to compare full policy objects directly.
+- It does not mutate sink state.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Drift Detection
+
+When diagnostics should report whether file policy changed after startup:
+```moonbit
+let unchanged = sink.policy_matches_default()
+```
+
+In this example, the direct sink exposes whether runtime file policy still matches the baseline.
+
+#### When Gate Reset Logic
+
+When code should only reset policy if drift exists:
+```moonbit
+if !sink.policy_matches_default() {
+  sink.reset_policy()
+}
+```
+
+In this example, policy reset only happens when runtime state diverged from defaults.
+
+### Error Case
+
+e.g.:
+- If callers need the exact differences instead of a boolean drift signal, they should inspect both `policy()` and `default_policy()`.
+
+- This helper only compares policy state; it does not report open, write, or flush failures.
+
+### Notes
+
+1. Use this helper for compact direct policy drift checks.
+
+2. It is especially useful before calling reset-style operations.