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BitLogger/docs/api/configured-logger-file-path-or-none.md
Nanaloveyuki 0e02f3d2cf 📝 Fix policy test and doc
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---
name: configured-logger-file-path-or-none
group: api
category: runtime
update-time: 20260707
description: Read the effective file path from a ConfiguredLogger only when it is actually file-backed.
key-word:
- logger
- runtime
- file
- truthful
---
## Configured-logger-file-path-or-none
Read the effective file path from a `ConfiguredLogger` only when it is actually file-backed.
This is the truthful companion to `file_path()`. Prefer it for diagnostics, branching, and recovery logic that must distinguish “not file-backed” from compatibility fallbacks.
### Interface
```moonbit
pub fn ConfiguredLogger::file_path_or_none(self : ConfiguredLogger) -> String? {}
```
#### input
- `self : ConfiguredLogger` - Config-driven runtime logger whose file path should be inspected.
#### output
- `String?` - `Some(path)` when the configured sink is file-backed, otherwise `None`.
### Explanation
Detailed rules explaining key parameters and behaviors
- File-backed sinks return `Some(path)` through the wrapped `RuntimeSink`.
- Queued file sinks forward the wrapped inner file sink path as `Some(path)`.
- Non-file sinks return `None`.
- This helper is observation-only and does not mutate logger state.
### How to Use
Here are some specific examples provided.
#### When Need Truthful File-backed Detection
When code should branch only if file semantics really exist:
```moonbit
match logger.file_path_or_none() {
Some(path) => println(path)
None => ()
}
```
In this example, `None` means the configured logger is not file-backed.
#### When Need Path Diagnostics Without Fallback Values
When support output should avoid compatibility placeholders:
```moonbit
let maybe_path = logger.file_path_or_none()
```
In this example, callers can keep “no file semantics” distinct from a real path.
### Error Case
e.g.:
- If the configured sink is not file-backed, the method returns `None`.
- If callers need the broader file snapshot or queue context, prefer `file_state_or_none()` or `file_runtime_state()`.
### Notes
1. Prefer this helper over `file_path()` for truthful runtime diagnostics.
2. `file_path()` remains available as the compatibility fallback API.