Derive Macro ExportMetrics 

#[derive(ExportMetrics)]
{
    // Attributes available to this derive:
    #[metric_prefix]
    #[help]
    #[otlp]
    #[clickhouse]
}

Derive macro for exporting metrics in Prometheus, DogStatsD, and OTLP formats.

Generates methods:

• export_prometheus(&self, output: &mut String) — Prometheus text format
• export_dogstatsd(&self, output: &mut String, tags: &[(&str, &str)]) — DogStatsD format
• export_dogstatsd_delta(...) — DogStatsD with per-sink delta temporality
• export_dogstatsd_with_temporality(...) — runtime-selectable cumulative or delta export
• export_otlp(...) — OTLP protobuf (only when #[otlp] attribute is present)
• export_clickhouse(...) — ClickHouse rows (only when #[clickhouse] attribute is present)

Supports unlabeled metrics (Counter, Gauge, GaugeF64, Histogram, Distribution, SampledTimer), compile-time labeled metrics (LabeledCounter<L>, LabeledGauge<L>, LabeledHistogram<L>, LabeledSampledTimer<L>), and runtime-labeled metrics (DynamicCounter, DynamicGauge, DynamicGaugeI64, DynamicHistogram, DynamicDistribution).

Example

use fast_telemetry::{Counter, Histogram, Gauge, LabeledCounter, DeriveLabel};

#[derive(Copy, Clone, Debug, DeriveLabel)]
#[label_name = "method"]
enum HttpMethod { Get, Post, Put, Delete }

#[derive(ExportMetrics)]
#[metric_prefix = "proxy"]
pub struct ProxyMetrics {
    #[help = "Total requests proxied"]
    pub requests: Counter,

    #[help = "Requests by HTTP method"]
    pub requests_by_method: LabeledCounter<HttpMethod>,

    #[help = "Request latency in microseconds"]
    pub latency: Histogram,

    #[help = "Current memory usage"]
    pub memory_mb: Gauge,
}

let metrics = ProxyMetrics::new();

// Prometheus export
let mut prom_output = String::new();
metrics.export_prometheus(&mut prom_output);

// DogStatsD export (with optional tags)
let mut statsd_output = String::new();
metrics.export_dogstatsd(&mut statsd_output, &[("env", "prod")]);