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BitLogger/docs/api/build-async-text-logger.md
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---
name: build-async-text-logger
group: api
category: async
update-time: 20260614
description: Build an async logger with a concrete text-console sink from combined logger and async config, using only the selected text-oriented LoggerConfig fields instead of the full sync build path.
key-word:
- async
- text
- builder
- public
---
## Build-async-text-logger
Build an async logger directly from `AsyncLoggerBuildConfig`, but keep the concrete sink type as `FormattedConsoleSink` instead of the broader runtime sink wrapper. This helper is the text-console specific counterpart to `build_async_logger(...)`.
### Interface
```moonbit
pub fn build_async_text_logger(config : AsyncLoggerBuildConfig) -> AsyncLogger[@bitlogger.FormattedConsoleSink] {
```
#### input
- `config : AsyncLoggerBuildConfig` - Combined sync logger config plus async queue and flush config.
#### output
- `AsyncLogger[FormattedConsoleSink]` - Config-built async logger backed by a concrete text console sink.
### Explanation
Detailed rules explaining key parameters and behaviors
- This builder converts `config.logger.sink.text_formatter` into a runtime `TextFormatter` and wires it into `text_console_sink(...)`.
- It always constructs a `FormattedConsoleSink` directly instead of branching on `config.logger.sink.kind`.
- The returned logger inherits `min_level`, `target`, and timestamp behavior from `config.logger`.
- Unlike `build_async_logger(...)`, this helper does not run the full synchronous `build_logger(config.logger)` path first.
- That means it uses `config.logger.sink.text_formatter`, `min_level`, `target`, and `timestamp` directly, but it does not apply `LoggerConfig.queue` or preserve other sync runtime sink controls.
- This builder returns the underlying `AsyncLogger[@bitlogger.FormattedConsoleSink]` value directly. `build_application_text_async_logger(...)` only re-exports that same result under the `ApplicationTextAsyncLogger` alias, while `build_library_async_text_logger(...)` wraps the same result in `LibraryAsyncLogger[@bitlogger.FormattedConsoleSink]`.
- This helper is best suited to text-console output paths where callers want the concrete formatted sink type instead of `RuntimeSink`.
- This async text path follows the same target story as the broader async library: `native / js / wasm / wasm-gc` have stronger local verification, while `llvm` remains experimental and locally unverified in this environment.
### How to Use
Here are some specific examples provided.
#### When Need Config-built Async Text Console Output
When async queue behavior is config-driven and output should stay on text console formatting:
```moonbit
let logger = build_async_text_logger(
AsyncLoggerBuildConfig::new(
logger=text_console(target="async.text"),
async_config=AsyncLoggerConfig::new(max_pending=4),
),
)
```
In this example, the async logger is built around a text console sink rather than the generic runtime sink enum.
### Error Case
e.g.:
- If callers need sink-kind-driven branching across console, JSON, text, or file output, `build_async_logger(...)` is the better fit.
- If the logger is never `run()`, pending records still follow the normal async queue lifecycle rules.
### Notes
1. This API is narrower than `build_async_logger(...)` because it preserves a concrete text sink type.
2. It is the base builder used by the application and library async text facades.
3. See [target-verification.md](./target-verification.md) for the current local verification matrix.
4. Use this direct builder when callers should keep the full async helper surface on the concrete text sink type rather than a naming alias or a narrowed library wrapper.