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Nanaloveyuki
112 lines
3.7 KiB
Markdown
112 lines
3.7 KiB
Markdown
---
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name: library-logger-log
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group: api
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category: facade
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update-time: 20260613
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description: Emit a record through a LibraryLogger facade with explicit level, message, fields, and optional target override by delegating to the wrapped logger.
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key-word:
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- library
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- facade
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- log
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- public
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---
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## Library-logger-log
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Emit a record through the library-facing sync logger with an explicit level and message. This is the core write API behind the level-specific `LibraryLogger` convenience methods.
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### Interface
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```moonbit
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pub fn[S : Sink] LibraryLogger::log(
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self : LibraryLogger[S],
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level : Level,
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message : String,
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fields~ : Array[Field] = [],
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target? : String = "",
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) -> Unit {
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```
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#### input
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- `self : LibraryLogger[S]` - Library-facing logger that should emit the record.
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- `level : Level` - Severity level for the record.
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- `message : String` - Log message text.
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- `fields : Array[Field]` - Optional structured fields attached to the record.
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- `target : String` - Optional per-call target override.
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#### output
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- `Unit` - No return value. The record is either skipped by level gating or written to the wrapped sink pipeline.
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### Explanation
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Detailed rules explaining key parameters and behaviors
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- This method delegates directly to the wrapped logger's `log(...)` behavior.
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- The logger checks `is_enabled(level)` before building and writing the record.
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- If `target` is empty, the facade's stored default target is used.
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- Any existing sink wrappers already inside the wrapped logger, such as `ContextSink`, `FilterSink`, `PatchSink`, or queued/runtime sink variants, still participate normally in the write path.
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- The narrower library facade does not change record construction semantics; it only limits the visible API surface.
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- Broader composition helpers remain on the underlying `Logger[S]` and require `to_logger()` first.
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### How to Use
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Here are some specific examples provided.
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#### When Need Full Per-call Control Through The Library Facade
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When library code should choose level, fields, and target explicitly:
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```moonbit
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logger.log(
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Level::Info,
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"worker started",
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fields=[field("job", "sync")],
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target="service.worker",
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)
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```
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In this example, the call site controls every major record property while keeping the narrower facade type.
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#### When Build Higher-level Library Wrappers
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When package code defines its own logging helpers:
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```moonbit
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fn log_retry(logger : LibraryLogger[ConsoleSink], attempt : Int) -> Unit {
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logger.log(Level::Warn, "retry scheduled", fields=[field("attempt", attempt.to_string())])
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}
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```
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In this example, `log(...)` acts as the shared primitive under custom library-facing wrappers.
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#### When Need Shared Context Plus Event-specific Fields
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When a facade already carries shared context but one write needs extra detail:
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```moonbit
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let logger = base.with_context_fields([field("service", "cache")])
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logger.log(
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Level::Info,
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"entry refreshed",
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fields=[field("key", "user:42")],
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)
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```
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In this example, both the stored shared context and the per-call fields still flow through the wrapped logger pipeline.
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### Error Case
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e.g.:
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- If `level` is below the current minimum threshold, the method returns without writing a record.
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- If `target` is empty and the logger default target is also empty, the emitted record simply has no target label.
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- If callers need broader composition helpers after writing, they must unwrap first with `to_logger()`.
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### Notes
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1. Use this API when the call site needs full control instead of a fixed-severity helper.
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2. The facade remains synchronous; any buffering behavior only comes from the wrapped sink type.
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3. Use the optional `target` argument when one write should temporarily override the facade's default target without rebuilding or rewrapping it.
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