Add support for Arc<T> to metrics::Cow<'a, T>. (#402)

metrics-tracing-context/src/lib.rs

@@ -107,8 +107,7 @@ pub use label_filter::LabelFilter;
 use tracing_integration::WithContext;
 pub use tracing_integration::{Labels, MetricsLayer};
 
-/// [`TracingContextLayer`] provides an implementation of a [`Layer`][metrics_util::layers::Layer]
-/// for [`TracingContext`].
+/// [`TracingContextLayer`] provides an implementation of a [`Layer`] for [`TracingContext`].
 pub struct TracingContextLayer<F> {
     label_filter: F,
 }

metrics-util/src/registry/mod.rs

@@ -32,17 +32,14 @@ type RegistryHashMap<K, V> = HashMap<K, V, BuildHasherDefault<RegistryHasher>>;
 /// ## Using `Registry` as the basis of an exporter
 ///
 /// As a reusable building blocking for building exporter implementations, users should look at
-/// [`Key`] and [`AtomicStorage`][crate::registry::AtomicStorage] to use for their key and storage,
-/// respectively.
+/// [`Key`] and [`AtomicStorage`] to use for their key and storage, respectively.
 ///
 /// These two implementations provide behavior that is suitable for most exporters, providing
 /// seamless integration with the existing key type used by the core
 /// [`Recorder`][metrics::Recorder] trait, as well as atomic storage for metrics.
 ///
-/// In some cases, users may prefer
-/// [`GenerationalAtomicStorage`][crate::registry::GenerationalAtomicStorage] when know if a metric
-/// has been touched, even if its value has not changed since the last time it was observed, is
-/// necessary.
+/// In some cases, users may prefer [`GenerationalAtomicStorage`] when know if a metric has been
+/// touched, even if its value has not changed since the last time it was observed, is necessary.
 ///
 /// ## Performance
 ///

metrics/CHANGELOG.md

@@ -8,6 +8,15 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased] - ReleaseDate
 
+### Added
+
+- Support for using `Arc<T>` with `Cow<'a, T>`.
+  ([#402](https://github.com/metrics-rs/metrics/pull/402))
+
+  This will primarily allow using `Arc<str>` for metric names and labels, where previously only
+  `&'static str` or `String` were allowed. There's still work to be done to also support labels in
+  this regard.
+
 ## [0.21.1] - 2023-07-02
 
 ### Added

metrics/src/common.rs

@@ -6,12 +6,15 @@ use crate::cow::Cow;
 
 /// An allocation-optimized string.
 ///
-/// We specify `SharedString` to attempt to get the best of both worlds: flexibility to provide a
-/// static or dynamic (owned) string, while retaining the performance benefits of being able to
-/// take ownership of owned strings and borrows of completely static strings.
+/// `SharedString` uses a custom copy-on-write implementation that is optimized for metric keys,
+/// providing ergonomic sharing of single instances, or slices, of strings and labels. This
+/// copy-on-write implementation is optimized to allow for constant-time construction (using static
+/// values), as well as accepting owned values and values shared through [`Arc<T>`](std::sync::Arc).
 ///
-/// `SharedString` can be converted to from either `&'static str` or `String`, with a method,
-/// `const_str`, from constructing `SharedString` from `&'static str` in a `const` fashion.
+/// End users generally will not need to interact with this type directly, as the top-level macros
+/// (`counter!`, etc), as well as the various conversion implementations
+/// ([`From<T>`](std::convert::From)), generally allow users to pass whichever variant of a value
+/// (static, owned, shared) is best for them.
 pub type SharedString = Cow<'static, str>;
 
 /// Key-specific hashing algorithm.