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Nanaloveyuki
99 lines
3.1 KiB
Markdown
99 lines
3.1 KiB
Markdown
---
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name: logger-log
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group: api
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category: logging
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update-time: 20260512
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description: Emit a record through the logger with an explicit level, message, optional fields, and optional target override.
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key-word:
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- logger
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- log
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- sync
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- public
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---
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## Logger-log
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Emit a record through the synchronous logger with an explicit level and message. This is the core write API behind all level-specific convenience methods.
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### Interface
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```moonbit
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pub fn[S : Sink] Logger::log(
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self : Logger[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 : Logger[S]` - 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 sink pipeline.
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### Explanation
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Detailed rules explaining key parameters and behaviors
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- The logger checks `is_enabled(level)` before building and writing the record.
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- If the level is disabled, the call returns without constructing a record or touching the sink pipeline.
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- If `target` is empty, the logger's stored default target is used.
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- If `target` is non-empty, it overrides the stored default target for that call only.
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- If timestamping is enabled, `@env.now()` is captured and stored in the emitted record.
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- The `fields` argument is attached to the constructed record first; context, filter, patch, and queue wrappers then act through the current sink pipeline after record construction.
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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
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When 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.
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And a per-call `target=` override affects only that write; later calls still fall back to the logger's stored target when no override is passed.
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#### When Build Higher-level Wrappers
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When application code defines its own logging helpers:
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```moonbit
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fn log_retry(logger : Logger[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 wrappers.
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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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### 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. This method is synchronous; any buffering behavior only comes from the wrapped sink type.
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3. If repeated call sites always use the same explicit target override, deriving a logger with `with_target(...)` or `child(...)` is usually clearer.
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