Trait castaway::LifetimeFree
source · pub unsafe trait LifetimeFree { }Expand description
Marker trait for types that do not contain any lifetime parameters. Such types are safe to cast from non-static type parameters if their types are equal.
This trait is used by cast! to determine what casts are legal on values
without a 'static type constraint.
§Safety
When implementing this trait for a type, you must ensure that the type is free of any lifetime parameters. Failure to meet all of the requirements below may result in undefined behavior.
- The type must be
'static. - The type must be free of lifetime parameters. In other words, the type must be an “owned” type and not contain any lifetime parameters.
- All contained fields must also be
LifetimeFree.
§Examples
use castaway::LifetimeFree;
struct Container<T>(T);
// UNDEFINED BEHAVIOR!!
// unsafe impl LifetimeFree for Container<&'static str> {}
// UNDEFINED BEHAVIOR!!
// unsafe impl<T> LifetimeFree for Container<T> {}
// This is safe.
unsafe impl<T: LifetimeFree> LifetimeFree for Container<T> {}
struct PlainOldData {
foo: u8,
bar: bool,
}
// This is also safe, since all fields are known to be `LifetimeFree`.
unsafe impl LifetimeFree for PlainOldData {}