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Nanaloveyuki
92 lines
3.2 KiB
Markdown
92 lines
3.2 KiB
Markdown
---
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name: library-logger-bind
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group: api
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category: facade
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update-time: 20260613
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description: Attach reusable structured fields to a LibraryLogger facade through the bind alias while extending the visible sink type to ContextSink.
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key-word:
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- library
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- facade
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- bind
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- public
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---
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## Library-logger-bind
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Attach shared structured fields to a `LibraryLogger[S]` through the `bind(...)` alias. This is behaviorally identical to `with_context_fields(...)` and exists as a shorter name for common library-facing context binding.
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### Interface
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```moonbit
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pub fn[S] LibraryLogger::bind(
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self : LibraryLogger[S],
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fields : Array[Field],
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) -> LibraryLogger[ContextSink[S]] {
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```
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#### input
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- `self : LibraryLogger[S]` - Base facade that should gain shared fields.
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- `fields : Array[Field]` - Structured fields attached to every emitted record.
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#### output
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- `LibraryLogger[ContextSink[S]]` - New library-facing wrapper that prepends shared fields at write time.
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### Explanation
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Detailed rules explaining key parameters and behaviors
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- `bind(...)` delegates directly to `with_context_fields(...)`.
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- Shared fields are applied to every later log call emitted through the returned facade.
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- The returned facade changes visible type from `LibraryLogger[S]` to `LibraryLogger[ContextSink[S]]` because the sink pipeline is extended with context-field merging behavior.
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- Minimum level, target, and timestamp behavior are preserved while the sink pipeline changes.
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- Broader composition helpers remain hidden behind the narrower facade after rewrapping; use `to_logger()` if later code needs them.
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- The original facade value is not mutated; a wrapped facade is returned.
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- This alias is useful when you prefer shorter chaining syntax in library code.
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### How to Use
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Here are some specific examples provided.
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#### When Bind Shared Package Context
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When a library logger should carry stable metadata through a flow:
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```moonbit
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let request_logger = default_library_logger()
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.with_target("sdk")
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.bind([field("request_id", "req-42")])
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```
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In this example, subsequent writes automatically include `request_id`.
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#### When Prefer Shorter Chaining Syntax
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When a context-bound child facade should stay readable:
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```moonbit
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let worker = LibraryLogger::new(console_sink(), target="app")
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.child("worker")
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.bind([field("component", "worker")])
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```
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In this example, `bind(...)` communicates intent without changing underlying behavior.
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And because it is only an alias, the resulting facade behaves the same as calling `with_context_fields(...)` directly.
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### Error Case
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e.g.:
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- If `fields` is empty, the returned facade remains valid and simply stores an empty shared field set in `ContextSink[S]`.
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- If duplicate field keys are bound, all copies are preserved for downstream formatting or inspection.
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- If callers want event-specific fields without changing the shared bound set, they should pass those through `log(..., fields=...)` on the returned facade.
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### Notes
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1. Use `bind(...)` and `with_context_fields(...)` interchangeably; choose the one that reads better in context.
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2. This alias exists for ergonomics, not for different semantics.
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3. Use `with_context_fields(...)` when the longer name makes the shared-field sink-type change clearer at the call site.
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