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 {}

Implementations on Foreign Types

Implementors