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| -rw-r--r-- | library/core/src/clone.rs | 40 |
1 files changed, 40 insertions, 0 deletions
diff --git a/library/core/src/clone.rs b/library/core/src/clone.rs index a6d6230d3a6..d7ca9c22dad 100644 --- a/library/core/src/clone.rs +++ b/library/core/src/clone.rs @@ -86,6 +86,46 @@ /// } /// ``` /// +/// If we `derive`: +/// +/// ``` +/// #[derive(Copy, Clone)] +/// struct Generate<T>(fn() -> T); +/// ``` +/// +/// the auto-derived implementations will have unnecessary `T: Copy` and `T: Clone` bounds: +/// +/// ``` +/// # struct Generate<T>(fn() -> T); +/// +/// // Automatically derived +/// impl<T: Copy> Copy for Generate<T> { } +/// +/// // Automatically derived +/// impl<T: Clone> Clone for Generate<T> { +/// fn clone(&self) -> Generate<T> { +/// Generate(Clone::clone(&self.0)) +/// } +/// } +/// ``` +/// +/// The bounds are unnecessary because clearly the function itself should be +/// copy- and cloneable even if its return type is not: +/// +/// ```compile_fail,E0599 +/// #[derive(Copy, Clone)] +/// struct Generate<T>(fn() -> T); +/// +/// struct NotCloneable; +/// +/// fn generate_not_cloneable() -> NotCloneable { +/// NotCloneable +/// } +/// +/// Generate(generate_not_cloneable).clone(); // error: trait bounds were not satisfied +/// // Note: With the manual implementations the above line will compile. +/// ``` +/// /// ## Additional implementors /// /// In addition to the [implementors listed below][impls], |