Add support for Arc<T> to metrics::Cow<'a, T>.

metrics-tracing-context/Cargo.toml

@@ -38,7 +38,7 @@ tracing-core = { version = "0.1.21", default-features = false }
 tracing-subscriber = { version = "0.3.1", default-features = false, features = ["std"] }
 
 [dev-dependencies]
-criterion = { version = "=0.3.3", default-features = false }
+criterion = "0.3"
 parking_lot = { version = "0.12.1", default-features = false }
 tracing = { version = "0.1.29", default-features = false, features = ["std"] }
 tracing-subscriber = { version = "0.3.1", default-features = false, features = ["registry"] }

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.