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Nanaloveyuki
80 lines
2.2 KiB
Markdown
80 lines
2.2 KiB
Markdown
---
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name: runtime-sink-file-policy-or-none
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group: api
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category: runtime
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update-time: 20260707
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description: Read the current runtime file policy from a RuntimeSink only when it is actually file-backed.
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key-word:
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- runtime
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- sink
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- file
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- truthful
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---
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## Runtime-sink-file-policy-or-none
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Read the current runtime file policy from a `RuntimeSink` only when it is actually file-backed.
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This is the truthful companion to `file_policy()`. Prefer it for diagnostics and recovery logic that must avoid fallback policy objects.
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### Interface
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```moonbit
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pub fn RuntimeSink::file_policy_or_none(self : RuntimeSink) -> FileSinkPolicy? {
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```
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#### input
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- `self : RuntimeSink` - Runtime sink whose current file policy should be inspected.
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#### output
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- `FileSinkPolicy?` - `Some(policy)` when the runtime sink is file-backed, otherwise `None`.
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### Explanation
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Detailed rules explaining key parameters and behaviors
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- Plain `File` runtime variants return `Some(current_policy)`.
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- `QueuedFile` runtime variants forward the wrapped inner file sink policy as `Some(current_policy)`.
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- Non-file runtime variants return `None`.
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- This helper is broader than `file_append_mode()` or `file_auto_flush()` because it returns the whole policy object without fallback synthesis.
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### How to Use
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Here are some specific examples provided.
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#### When Need Truthful Policy Diagnostics
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When diagnostics should inspect file policy only if file semantics exist:
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```moonbit
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match sink.file_policy_or_none() {
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Some(policy) => ignore(policy)
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None => ()
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}
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```
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In this example, `None` means there is no real file policy to inspect.
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#### When Need Compatibility-free Recovery Decisions
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When recovery logic should not treat a fallback object as real state:
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```moonbit
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let maybe_policy = sink.file_policy_or_none()
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```
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In this example, callers can distinguish missing file semantics from a live policy snapshot.
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### Error Case
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e.g.:
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- If the runtime sink is not file-backed, the method returns `None`.
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- If callers need default-policy comparison, pair it with `file_default_policy_or_none()`.
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### Notes
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1. Prefer this helper over `file_policy()` for truthful runtime diagnostics.
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2. `file_policy()` remains available as the compatibility fallback API.
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