Enum wnf::SeenChangeStamp

pub enum SeenChangeStamp {
    None,
    Current,
    Value(ChangeStamp),
}

Available on crate feature subscribe only.

The change stamp that a state listener has last seen

The OwnedState::subscribe and BorrowedState::subscribe methods expect an argument of this type to indicate what change stamp of the state the listener has last seen. The listener will then only be notified about updates with a (strictly) larger change stamp, i.e. updates that happen after the one it has last seen.

Variants

None

Indicates that a listener has not seen any change stamp

When subscribing with this value, the listener will be notified once about the current data of the state (only if any data has been written to the state yet) and then again once about each future state update.

This is most useful for listeners that track the data of the state, e.g. for showing it in a UI, because it eliminates the need for a separate query for the current data before subscribing.

Current

Indicates that a listener has seen the current change stamp

When subscribing with this value, the listener will be notified once about each future state update, but not about the current data of the state.

This is most useful for listeners that treat updates to the state data as events, e.g. for logging, because it ensures that they are only called when an actual update happens.

Value(ChangeStamp)

Indicates that a listener has seen a change stamp with a particular value

When subscribing with this value, the listener will be notified once about each state update whose change stamp is strictly larger than the given change stamp. The earliest possible notification is for the current data of the state (only if any data has been written to the state yet), i.e. it will never be notified about past state updates regardless of the passed value.

This is most useful if you have queried the state data before and are already holding a change stamp.

Trait Implementations

impl Clone for SeenChangeStamp

fn clone(&self) -> SeenChangeStamp

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for SeenChangeStamp

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

Formats the value using the given formatter.

impl Default for SeenChangeStamp

fn default() -> SeenChangeStamp

Returns the “default value” for a type.

impl Hash for SeenChangeStamp

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)where
    H: Hasher,
    Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq<SeenChangeStamp> for SeenChangeStamp

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

This method tests for self and other values to be equal, and is used by ==.

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

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

impl Copy for SeenChangeStamp

impl Eq for SeenChangeStamp

impl StructuralEq for SeenChangeStamp

impl StructuralPartialEq for SeenChangeStamp