Function contract_check_ensures 

pub const fn contract_check_ensures<C: Fn(&Ret) -> bool + Copy, Ret>(
    cond: Option<C>,
    ret: Ret,
) -> Ret

🔬This is a nightly-only experimental API. (contracts_internals #128044)

Check if the post-condition cond has been met.

By default, if contract_checks is enabled, this will panic with no unwind if the condition returns false.

If cond is None, then no postcondition checking is performed.

Note that this function is a no-op during constant evaluation.