feat: impl<T: Collector> Collector for std::sync::Arc<T> (prometheus#273)

Signed-off-by: hanabi1224 <[email protected]>

Author: hanabi1224

CHANGELOG.md

@@ -14,9 +14,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `Family::get_or_create_owned` can access a metric in a labeled family. This
    method avoids the risk of runtime deadlocks at the expense of creating an
    owned type. See [PR 244].
+
+- `impl<T: Collector> Collector for std::sync::Arc<T>`.
+   See [PR 273].
 
 [PR 244]: https://github.com/prometheus/client_rust/pull/244
 [PR 257]: https://github.com/prometheus/client_rust/pull/257
+[PR 273]: https://github.com/prometheus/client_rust/pull/273
 
 ### Changed
 

src/collector.rs

@@ -39,3 +39,9 @@ pub trait Collector: std::fmt::Debug + Send + Sync + 'static {
     /// Once the [`Collector`] is registered, this method is called on each scrape.
     fn encode(&self, encoder: DescriptorEncoder) -> Result<(), std::fmt::Error>;
 }
+
+impl<T: Collector> Collector for std::sync::Arc<T> {
+    fn encode(&self, encoder: DescriptorEncoder) -> Result<(), std::fmt::Error> {
+        self.as_ref().encode(encoder)
+    }
+}