Custom attributes
The Copy and Clone traits support the following attributes:
- Container attributes
- Field attributes
clone_from
The Clone trait has a default implementation for clone_from and
derive(Clone) never implements that method. derivative can implement it if
asked explicitly.
Note that while the generated implementation is good for structures, it might
not be very efficient for enumerations. What it does is check if both self
and the clone-from value have the same variant, if they have, use clone_from
on the members, otherwise fallback to *self = other.clone();. Ask yourself if
you really need this.
Custom bound
As most other traits, Copy and Debug support a custom bound on container
and fields. See Debug's documentation for more
information.
Limitations
rustc can optimize derive(Clone, Copy) to generate faster, smaller code.
So does derivative. But rustc does not know about derivative(Copy) and
would not optimize #[derivative(Copy)] #[derive(Clone)].
To avoid that issue, you should avoid deriving Clone using rustc's default
derive and Copy using derivative. derivative will error if it detects
that, but can't always do it.