Macro CovariantForLt 

CovariantForLt!() { /* proc-macro */ }

Obtain a type that implements CovariantForLt (and ForLt) for the given higher-ranked type.

Unlike ForLt!, this macro additionally proves that the type is covariant over the lifetime, providing a safe CovariantForLt::cast_ref method.

Please refer to the documentation of the CovariantForLt trait.