---
name: application-logger
group: api
category: facade
update-time: 20260613
description: Application-facing alias for the configured sync runtime logger surface, preserving the full ConfiguredLogger helper set.
key-word:
    - application
    - facade
    - alias
    - public
---

## Application-logger

`ApplicationLogger` is the application-facing sync logger alias. It currently maps directly to `ConfiguredLogger` and keeps the same runtime helper surface for sync logging, queue inspection, and file controls.

### Interface

```moonbit
pub type ApplicationLogger = ConfiguredLogger
```

#### output

- `ApplicationLogger` - Application-facing name for the configured sync runtime logger shape.

### Explanation

Detailed rules explaining key parameters and behaviors

- This alias does not introduce a new runtime type or wrapper layer.
- It preserves the same logging, queue, and file helper APIs exposed by `ConfiguredLogger`.
- Because `ConfiguredLogger` is itself `Logger[RuntimeSink]`, the alias also keeps ordinary logger composition and write behavior such as `with_target(...)`, `child(...)`, and `log(..., target=...)`.
- In particular, `log(..., target=...)` can override the target for one call, while severity helpers such as `info(...)`, `warn(...)`, and `error(...)` continue using the stored logger target unless code derives another logger first with `with_target(...)` or `child(...)`.
- Like the underlying synchronous logger line, `with_context_fields(...)` and `bind(...)` do not preserve the alias spelling. They return a `Logger[ContextSink[RuntimeSink]]` shape because sync shared-field binding extends the sink pipeline instead of storing extra alias-level context metadata.
- Because this is only an alias, the application-facing type does not hide any configured-runtime helpers or broader logger surface.
- That means queue, drain, flush, and file runtime helpers remain directly callable on `ApplicationLogger` itself; callers do not need an unwrap step to reach the underlying configured runtime logger behavior.
- The alias exists to give application boot code a clearer public entry name.
- Builders such as `build_application_logger(...)` and `parse_and_build_application_logger(...)` return this alias.

### How to Use

Here are some specific examples provided.

#### When Need An App-level Name For The Configured Runtime Logger

When application code wants a stable public type name for the configured sync logger:
```moonbit
let logger : ApplicationLogger = build_application_logger(LoggerConfig::new(target="app"))
```

In this example, the application alias keeps the same underlying runtime logger behavior while presenting an app-facing type name.

#### When Pass The Configured Logger Through App-level APIs

When top-level boot code or services should expose an application-oriented logger type:
```moonbit
fn start(logger : ApplicationLogger) -> Unit {
  logger.info("started")
}
```

In this example, callers see the app-facing alias instead of the lower-level `ConfiguredLogger` name.

And the same queue/file/runtime helpers remain directly callable because no narrowing wrapper is added.

#### When Need Direct Runtime Helpers On The Application Alias

When app code should inspect queue state or file controls without leaving the alias surface:
```moonbit
ignore(logger.pending_count())
ignore(logger.flush())
```

In this example, the runtime helpers are called directly on `ApplicationLogger`.

And unlike `LibraryLogger[RuntimeSink]`, no `to_logger()` unwrap is required first.

And the inherited logger target rules stay the same: `log(..., target=...)` can override the target per call, while `info(...)`, `warn(...)`, and `error(...)` continue using the stored target unless code derives another logger first with `with_target(...)` or `child(...)`.

#### When Need A One-call Target Override Without Rebuilding The Alias

When app-level sync code should keep the same alias value but emit one record under a different target:
```moonbit
logger.log(Level::Error, "boom", target="app.audit")
```

In this example, the emitted record uses `app.audit` only for that one call.

And later `info(...)`, `warn(...)`, or `error(...)` calls still use the alias value's stored target unless code derives another logger first with `with_target(...)` or `child(...)`.

#### When Need Shared Context On The Sync Application Alias

When app-level sync code should attach stable metadata to later records:
```moonbit
let contextual = logger.with_context_fields([field("service", "billing")])
```

In this example, the returned value has the visible type `Logger[ContextSink[RuntimeSink]]` rather than the alias name `ApplicationLogger`.

And that type-shape change is expected because sync context binding extends the sink pipeline.

### Error Case

e.g.:
- Because this is only an alias, any backend limitations of `ConfiguredLogger` still apply unchanged.

- If code needs a narrower public surface than the full configured runtime logger, `LibraryLogger` is the better facade.

### Notes

1. This alias is about naming and public intent, not a different runtime implementation.

2. Inherited `Logger` behavior stays unchanged on this alias, including target overrides on `log(...)` and derived target composition through `with_target(...)` and `child(...)`.

3. Use `build_application_logger(...)` or `parse_and_build_application_logger(...)` for the usual construction paths.

4. Use `LibraryLogger` instead when a library boundary should intentionally hide configured-runtime helper methods behind a narrower facade.