feat: const-default_1 Cargo feature

Author: yvt

CHANGELOG.md

@@ -6,6 +6,11 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+
+### Added
+
+- `const-default_1` Cargo feature, which enables the implementation of [`ConstDefault`](https://docs.rs/const-default/1.0.0/const_default/trait.ConstDefault.html) from [`const-default ^1`](https://crates.io/crates/const-default/1.0.0).
+
 ## [0.3.5] - 2021-09-04
 
 ### Added

Cargo.toml

@@ -25,6 +25,12 @@ maintenance = { status = "passively-maintained" }
 [dependencies]
 spin = { version = "0.9.2", optional = true }
 
+[dependencies.const-default_1]
+package = "const-default"
+version = "1"
+optional = true
+default-features = false
+
 [dev-dependencies]
 rayon = "1.5.1"
 futures = "0.3.17"

README.md

@@ -256,6 +256,10 @@ let _ = token_1;
  - **`alloc`** enables the items that depend on `alloc`.
  - **`unstable`** enables experimental items that are not subject to the
    semver guarantees.
+ - **`const-default_1`** enables the implementation of `ConstDefault` from
+   [`const-default ^1`][].
+
+[`const-default ^1`]: https://crates.io/crates/const-default/1.0.0
 
 ## Related Work
 

src/lib.rs

@@ -286,6 +286,10 @@
 //!  - **`alloc`** enables the items that depend on `alloc`.
 //!  - **`unstable`** enables experimental items that are not subject to the
 //!    semver guarantees.
+//!  - **`const-default_1`** enables the implementation of `ConstDefault` from
+//!    [`const-default ^1`][].
+//!
+//! [`const-default ^1`]: https://crates.io/crates/const-default/1.0.0
 //!
 //! # Related Work
 //!
@@ -550,6 +554,17 @@ macro_rules! impl_common {
             }
         }
 
+        #[cfg(feature = "const-default_1")]
+        impl<
+            T: const_default_1::ConstDefault,
+            Keyhole: const_default_1::ConstDefault
+        > const_default_1::ConstDefault for $ty<T, Keyhole> {
+            const DEFAULT: Self = Self {
+                keyhole: const_default_1::ConstDefault::DEFAULT,
+                data: const_default_1::ConstDefault::DEFAULT,
+            };
+        }
+
         /// # Construction and Destruction
         ///
         impl<T, Keyhole> $ty<T, Keyhole> {