Trait lifelink::Cov

pub unsafe trait Cov: Ctor {
    // Required method
    fn cov<'r, 'a, 'b>(r: &'r Self::Ty<'a>) -> &'r Self::Ty<'b>
       where 'a: 'b;
}

Trait for type constructors that produce types whose references are covariant over the lifetime parameter.

For most valid types, this could implemented by simply invoking cov!:

struct FooCtor;
struct Foo<'a>(&'a u8);
impl Ctor for FooCtor {
    type Ty<'a> = Foo<'a>;
}

cov!(FooCtor);

Safety

References to types produced by this type constructor must be covariant over the lifetime parameter.

This trait is unsafe for the reason that it is trivial to write a type-checking implementation of cov for every type out there, simply by writing panic!(). Lifetime variance is hard to figure out in a complex type. It’s safest to use the cov! macro for applicable types, unless you are really sure that you know better than the compiler.

Required Methods

fn cov<'r, 'a, 'b>(r: &'r Self::Ty<'a>) -> &'r Self::Ty<'b>where 'a: 'b,

Implementors

impl<T: 'static> Cov for RefCtor<T>