Enum BorrowKind 

#[non_exhaustive]
pub enum BorrowKind {
    Untracked,
    Shared,
    Unique,
    Owning,
    UniquePinning,
}

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Untracked

Other borrows are allowed (like *mut T and RcRef<T>).

Shared

Other Shared simultaneous borrows are allowed (like &T).

Unique

No other simultaneous tracked borrows are allowed (like &mut T).

Owning

No other simultaneous or subsequent borrows are allowed (like &own T).

UniquePinning

No other simultaneous tracked borrows are allowed and drop must be called before the underlying memory is reclaimed (like &pin mut T).