Method StateCell

Namespace

SodaFlow.Collections

Assembly

SodaFlow.Collections.dll

StateCell<TKey, TIdentity, TState>(ReactiveCollection<TKey, TIdentity, TState>, TKey)

A cell that follows the mutable part of one item. It has no value while the store does not have the key.

public static Cell<Maybe<TState>> StateCell<TKey, TIdentity, TState>(this ReactiveCollection<TKey, TIdentity, TState> collection, TKey key) where TKey : notnull where TIdentity : notnull

Parameters

collection ReactiveCollection<TKey, TIdentity, TState>

The collection or view to monitor.

key TKey

The key to monitor.

Returns

Cell<Maybe<TState>>

A cell tracking that key's state.

Type Parameters

TKey

The type of the keys.

TIdentity

The type of the immutable part of an item.

TState

The type of the mutable part of an item.

Remarks

The cost is low, thus code can make one for each bound view. It filters on one hash lookup and does not read the other items. A weak cache holds one for each key, thus N observers of one key share a node, and two views of the same root give the same cell.

The key can be missing now. A removal sends no value, and a subsequent add with the same key sends a value again. Thus, a view that binds to a key can continue after the item.

This answers for the store and not for the members of a view. A read of a filtered view for a key that its filter removed gives the state of that item. KeysCell answers for the members.