Struct CompareAndSwap 

pub struct CompareAndSwap<'swap> {
    pub target_ref: &'swap str,
    pub detached: bool,
    pub nonce: &'swap str,
    pub new_oid: &'swap str,
    pub expected_old: &'swap Base,
    pub hash_length: usize,
}

What: One compare-and-swap of a landing’s target. Why: Grouping the facts keeps the call site readable and names what the swap depends on.

In TS you’d write (pseudocode):

{ targetRef, symbolicHead, transactionId, newOid, expectedOld, emptyTreeOid }

Fields

target_ref: &'swap str

Ref to move: the branch, or HEAD when detached.

detached: bool

Whether HEAD is detached, so --no-deref moves HEAD itself.

nonce: &'swap str

Transaction ID written into the reflog message.

new_oid: &'swap str

Commit to land.

expected_old: &'swap Base

Value the target must still hold.

hash_length: usize

Hash length in hex digits, which sets the width of the all-zero unborn value.