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BitLogger/docs/api/library-logger-to-logger.md
2026-06-14 14:00:00 +08:00

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---
name: library-logger-to-logger
group: api
category: facade
update-time: 20260614
description: Recover the underlying full sync logger from the library-facing sync facade without rebuilding, copying, or detaching the wrapped logger state.
key-word:
- logger
- library
- facade
- public
---
## Library-logger-to-logger
Recover `Logger[S]` from `LibraryLogger[S]`. This unwraps the library-facing sync facade when code needs methods that are only available on the full logger type.
### Interface
```moonbit
pub fn[S] LibraryLogger::to_logger(self : LibraryLogger[S]) -> Logger[S] {}
```
#### input
- `self : LibraryLogger[S]` - Library-facing sync logger facade.
#### output
- `Logger[S]` - The underlying full sync logger.
### Explanation
Detailed rules explaining key parameters and behaviors
- This conversion unwraps the existing logger instead of rebuilding it.
- Sink wiring, target, min level, timestamp behavior, and attached wrappers remain the same.
- The returned `Logger[S]` is still that same live wrapped value, so later facade writes or later unwraps continue observing and mutating the same logger instance.
- Use this when code needs full-surface APIs such as `with_timestamp(...)`, `with_filter(...)`, or `with_patch(...)`.
- When the wrapped sink is `RuntimeSink`, unwrapping preserves that runtime sink value, but the result type is still `Logger[RuntimeSink]` rather than the `ConfiguredLogger` alias. Runtime-specific operations remain available through `full.sink` or by keeping a `ConfiguredLogger` value directly.
- That same unwrap also preserves queued runtime state and file-backed helper behavior exactly as they existed behind the facade, including drain or flush results, file state snapshots, and file control methods.
- Runtime and file helper mutations are still live too. Draining queued records, flushing, or changing file helper state through the unwrapped logger changes the same runtime-backed logger that the facade already wrapped.
### How to Use
Here are some specific examples provided.
#### When Need Full Logger-only Composition APIs
When a library-facing logger must be widened temporarily for additional composition:
```moonbit
let library_logger = LibraryLogger::new(console_sink(), target="lib")
let full_logger = library_logger.to_logger().with_timestamp()
```
In this example, the facade is unwrapped so the caller can access full logger composition APIs again.
#### When Need Runtime Helpers After Library-oriented Config Build
When a library-facing runtime logger should later expose configured runtime controls internally:
```moonbit
let full = logger.to_logger()
ignore(full.sink.pending_count())
```
In this example, unwrapping preserves the same `RuntimeSink` pipeline, and callers reach runtime-specific helpers through that preserved sink value.
The same handle keeps reflecting later facade writes instead of becoming a detached snapshot.
### Error Case
e.g.:
- If callers only need library-oriented write APIs, unwrapping is unnecessary.
- Unwrapping does not change the current target or sink behavior by itself.
- Recovering the full logger does not rebuild or reset the existing sink wrappers.
- Recovering the full logger does not translate configured runtime state into a simpler snapshot; queued counts, file availability, file failure counters, and runtime file controls stay exactly as they were on the wrapped logger.
- Recovering the full logger also does not isolate later runtime-helper mutations. If unwrapped code drains queued records or changes file helper state, later facade writes still run against that same updated wrapped logger.
### Notes
1. Use this only when the narrower facade is no longer sufficient.
2. This is the inverse projection of `Logger::to_library_logger()`.
3. Use `LibraryLogger[S]` directly when the narrower package-facing surface is still sufficient.