lyng/docs/ObservableList.md

ObservableList module

ObservableList lives in explicit module lyng.observable.

Import it first:

import lyng.observable
>>> void

Create from a regular mutable list:

import lyng.observable
val xs = [1,2,3].observable()
assert(xs is ObservableList<Int>)
assertEquals([1,2,3], xs)
>>> void

Hook flow

Event order is:

1. beforeChange(change) listeners
2. mutation commit
3. onChange(change) listeners
4. changes() flow emission

Rejection is done by throwing in beforeChange.

import lyng.observable
val xs = [1,2].observable()
xs.beforeChange {
    throw ChangeRejectionException("no mutation")
}
assertThrows(ChangeRejectionException) { xs += 3 }
assertEquals([1,2], xs)
>>> void

Subscriptions

beforeChange and onChange return Subscription. Call cancel() to unsubscribe.

import lyng.observable
val xs = [1].observable()
var hits = 0
val sub = xs.onChange { hits++ }
xs += 2
sub.cancel()
xs += 3
assertEquals(1, hits)
>>> void

Change events

changes() returns Flow<ListChange<T>> with concrete event classes:

• ListInsert

• ListSet

• ListRemove

• ListClear

• ListReorder

  import lyng.observable val xs = [10,20].observable() val it = xs.changes().iterator() xs[1] = 200 val ev = it.next() assert(ev is ListSet) assertEquals(20, (ev as ListSet).oldValue) assertEquals(200, ev.newValue) it.cancelIteration()

  void