Macro span 

macro_rules! span {
    ($name:expr) => { ... };
    ($name:expr, kind = $kind:expr) => { ... };
    ($name:expr, $($key:expr => $value:expr),+ $(,)?) => { ... };
    ($name:expr, kind = $kind:expr, $($key:expr => $value:expr),+ $(,)?) => { ... };
}

Helper macro for creating instrumented spans.

Example

use crate::telemetry::span;

let span = span!("process_event", kind = SpanKind::Internal, "event.type" => "metric");