📝 document runtime sink file policies

2026-07-29 22:16:34 +00:00 · 2026-06-13 23:16:37 +08:00
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+---
+name: runtime-sink-file-policy-matches-default
+group: api
+category: runtime
+update-time: 20260613
+description: Read whether the current runtime file policy still matches the RuntimeSink default policy.
+key-word:
+    - runtime
+    - sink
+    - file
+    - public
+---
+
+## Runtime-sink-file-policy-matches-default
+
+Read whether the current runtime file policy still matches the default policy of a `RuntimeSink`. This helper is useful for detecting operational drift on direct sink values.
+
+### Interface
+
+```moonbit
+pub fn RuntimeSink::file_policy_matches_default(self : RuntimeSink) -> Bool {
+```
+
+#### input
+
+- `self : RuntimeSink` - Runtime 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
+
+- Plain `File` runtime variants compare current runtime file policy against their stored defaults.
+- `QueuedFile` runtime variants forward the comparison from the wrapped inner `FileSink`.
+- Non-file runtime variants return `false`.
+- This helper is a compact drift signal when callers do not need to compare full policy objects directly.
+
+### 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.file_policy_matches_default()
+```
+
+In this example, the runtime 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.file_policy_matches_default() {
+  ignore(sink.file_reset_policy())
+}
+```
+
+In this example, policy reset only happens when runtime state diverged from defaults.
+
+### Error Case
+
+e.g.:
+- If the runtime sink is not file-backed, the method returns `false`.
+
+- If callers need the exact differences instead of a boolean drift signal, they should inspect both `file_policy()` and `file_default_policy()`.
+
+### Notes
+
+1. Use this helper for compact runtime policy drift checks.
+
+2. It is especially useful before calling reset-style operations.