`#[derive]` sometimes uses incorrect bounds (aka lack of "perfect derive")

<!-- homu-ignore:start --> *[View all comments](https://triagebot.infra.rust-lang.org/gh-comments/rust-lang/rust/issues/26925)* <!-- homu-ignore:end --> In the following code: ```rs #[derive(Copy, Clone)] struct Y<T>(&'static fn(T)); ``` both derives expand to impls that require the corresponding trait to be implemented on the type parameter, e.g.: ```rs #[automatically_derived] impl<T: ::std::marker::Copy> ::std::marker::Copy for Y<T> where T: ::std::marker::Copy {} ``` However, this isn't actually necessary, as `Y<T>` will still be eligible for `Copy` regardless of whether `T` is. This may be hard to fix, given the compilation phase at which `#[derive]` works...

Posted by comex on Jul 9, 2015, 9:58 PM

Tags

• ux (Sysadmin)

Related issues

• [Codex Desktop][Windows] Weekly quota jumped 67 points in 38 seconds (Oct 16, 2026; 18:10 UTC)
• I loathe how difficult Matrix is for normal people though.
• Fragile against upgrades, tons of unmaintained plugins, admin panel UX is a mess where you struggle to find the stuff your are looking fo...
• Unfortunately there doesn’t seem to be any decent alternative.
• I'm wondering how much of that is bad developer UX and defaults, and how much of that is inherent complexity in the problem space.
• Pulumi support