📝 document runtime sink append path methods

2026-07-27 02:12:18 +00:00 · 2026-06-13 22:59:12 +08:00
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+---
+name: runtime-sink-file-append-mode
+group: api
+category: runtime
+update-time: 20260613
+description: Read the current append-mode policy used by a file-backed RuntimeSink.
+key-word:
+    - runtime
+    - sink
+    - file
+    - public
+---
+
+## Runtime-sink-file-append-mode
+
+Read the current append-mode policy used by a file-backed `RuntimeSink`. This helper exposes whether future reopen behavior is currently append-oriented on the runtime sink itself.
+
+### Interface
+
+```moonbit
+pub fn RuntimeSink::file_append_mode(self : RuntimeSink) -> Bool {
+```
+
+#### input
+
+- `self : RuntimeSink` - Runtime sink 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
+
+- Plain `File` runtime variants report the current append policy from the wrapped `FileSink`.
+- `QueuedFile` runtime variants forward the policy from the wrapped inner `FileSink`.
+- Non-file runtime variants 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 Direct Runtime Append-policy Visibility
+
+When diagnostics should show how future reopen behavior is configured on a `RuntimeSink`:
+```moonbit
+let append = sink.file_append_mode()
+```
+
+In this example, the runtime sink exposes current reopen policy directly.
+
+#### When Validate Direct Policy Changes
+
+When policy mutation should be observable after a direct setter call:
+```moonbit
+ignore(sink.file_set_append_mode(true))
+ignore(sink.file_append_mode())
+```
+
+In this example, callers verify the updated append-mode policy on the runtime sink itself.
+
+### Error Case
+
+e.g.:
+- If the runtime 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 direct runtime file behavior.