📝 document file sink policy accessors

2026-07-31 23:44:39 +00:00 · 2026-06-13 22:16:32 +08:00
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+---
+name: file-sink-append-mode
+group: api
+category: sink
+update-time: 20260613
+description: Read the current append-mode policy used by a FileSink.
+key-word:
+    - file
+    - sink
+    - append
+    - public
+---
+
+## File-sink-append-mode
+
+Read the current append-mode policy used by a `FileSink`. This helper exposes whether future reopen behavior is currently append-oriented for the concrete sink value.
+
+### Interface
+
+```moonbit
+pub fn FileSink::append_mode(self : FileSink) -> Bool {
+```
+
+#### input
+
+- `self : FileSink` - File sink whose current append-mode policy should be inspected.
+
+#### output
+
+- `Bool` - Current append-mode policy for the sink.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- This method reads the sink's current runtime append policy.
+- The value affects later `reopen(...)` behavior.
+- It does not report whether a file is currently writable or available.
+- This helper does not mutate sink state.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Direct Append-policy Visibility
+
+When diagnostics should show how future reopen behavior is configured:
+```moonbit
+let append = sink.append_mode()
+```
+
+In this example, the concrete file sink exposes its current append policy directly.
+
+#### When Validate Policy Updates
+
+When a setter call should be observed immediately:
+```moonbit
+sink.set_append_mode(true)
+ignore(sink.append_mode())
+```
+
+In this example, callers verify the updated append-mode policy on the sink itself.
+
+### Error Case
+
+e.g.:
+- If callers need the full current file policy rather than just append mode, `policy()` is the better API.
+
+- This helper alone does not prove the sink is currently open; use `is_available()` for that.
+
+### 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 file-sink behavior.