Async-logger-child

Create a child async logger by composing the current target with another target segment. This is the standard API for hierarchical async logger naming such as app.worker or service.http.client.

Interface

pub fn[S] AsyncLogger::child(self : AsyncLogger[S], target : String) -> AsyncLogger[S] {}

input

• self : AsyncLogger[S] - Parent async logger whose target should be extended.
• target : String - Child target segment or suffix.

output

• AsyncLogger[S] - A new async logger value whose default target is the composed child path.

Explanation

Detailed rules explaining key parameters and behaviors

• The returned logger is derived from self; the original async logger value is not mutated.
• If the parent target is empty, the child target becomes the full target.
• If the child target is empty, the parent target is preserved.
• If both are non-empty, they are joined with ..
• Only the stored target changes. Queue settings, sink wiring, flush policy, level gating, and lifecycle state remain shared with the same underlying async logger setup.
• In the current direct async coverage, timestamp is also preserved on the derived child logger while the source logger keeps its previous parent target.

How to Use

Here are some specific examples provided.

When Need Hierarchical Async Targets

When subsystem logs should stay grouped under one async namespace:

let logger = async_logger(console_sink(), target="service")
let worker = logger.child("worker")

In this example, worker emits under service.worker while keeping the same async queue behavior.

And logger still keeps its original stored target, because child(...) returns a derived async logger value instead of mutating the parent.

When Build Deep Async Scopes Step By Step

When deeper target composition should remain readable:

let http = async_logger(console_sink(), target="app")
  .child("http")
  .child("client")

In this example, the final logger target becomes app.http.client.

Error Case

e.g.:

• If target is empty, the returned logger keeps the original parent target.

• If callers need complete replacement rather than composition, with_target(...) should be used instead.

Notes

1. This is the preferred API for hierarchical async logger naming.

2. Composition changes the target only and does not rebuild the queue or sink.

3. State helpers such as pending_count(), dropped_count(), is_closed(), and has_failed() still operate on the same async logger state after derivation.

4. Use child("") when code should keep the current target while still following a target-composition code path.