pub const fn variance<T>() -> Twhere
    T: Variance,🔬This is a nightly-only experimental API. (
phantom_variance_markers #135806)Expand description
Construct a variance marker; equivalent to Default::default.
This type can be any of the following. You generally should not need to explicitly name the type, however.
- PhantomCovariant
- PhantomContravariant
- PhantomInvariant
- PhantomCovariantLifetime
- PhantomContravariantLifetime
- PhantomInvariantLifetime
§Example
#![feature(phantom_variance_markers)]
use core::marker::{PhantomCovariant, variance};
struct BoundFn<F, P, R>
where
    F: Fn(P) -> R,
{
    function: F,
    parameter: P,
    return_value: PhantomCovariant<R>,
}
let bound_fn = BoundFn {
    function: core::convert::identity,
    parameter: 5u8,
    return_value: variance(),
};