Enum RefPrecondition 

pub enum RefPrecondition {
    Any,
    MustExist,
    MustNotExist,
    MustExistAndMatch(RefTarget),
    ExistingMustMatch(RefTarget),
}

The compare-and-swap precondition a ref update is checked against (re-verified while the ref is locked, so it is a true CAS, not a check-then-write).

RefUpdate::expected can express Any (None) and MustExistAndMatch (Some); the create-only and match-or-create modes are reachable via FileRefTransaction::update_to.

Variants

Any

No precondition: create or overwrite unconditionally.

MustExist

The ref must currently exist (with any value).

MustNotExist

The ref must currently not exist (create-only).

MustExistAndMatch(RefTarget)

The ref must currently exist and point exactly at this target.

ExistingMustMatch(RefTarget)

If the ref exists it must point exactly at this target; if it is absent, the update is still allowed (match-or-create).

Trait Implementations

impl Clone for RefPrecondition

fn clone(&self) -> RefPrecondition

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for RefPrecondition

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for RefPrecondition

impl PartialEq for RefPrecondition

fn eq(&self, other: &RefPrecondition) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl StructuralPartialEq for RefPrecondition