Macro span 

macro_rules! span {
    ($name:expr) => { ... };
    ($name:expr, $($field:tt)*) => { ... };
}

Conditional span creation macro - compiles to no-op when profiling is disabled.

Example

use edgefirst_client::span;

fn process_data() {
    let _span = span!("process_data", items = 100);
    // ... processing
}