Macro gauge 

macro_rules! gauge {
    ($metric:ident $(. $suffixes:ident)*  = $metric_value:expr $(, $attrs:ident=$values:expr)*) => { ... };
}

Records an increment to the named monotonic counter with the given attributes.

The increment may only be a positive i64 or f64. You must not mix types for the same metric.

Takes advantage of gauge support in tracing-opentelemetry.

gauge!(spin.metric_name = 1, metric_attribute = "value");