Rx.Observable.prototype.distinctUntilChanged のおかしな挙動

distinct-test.coffee

describe 'distinctUntilChanged', ->
  it 'comparer', ->
    isEqual = require 'lodash.isequal'
    subjectX = new Rx.Subject()
    subjectX
    .distinctUntilChanged null, isEqual
    .toArray()
    .subscribe (a) ->
      # currentKey was updated by `o.value = 2`
      assert a.length is 1
      [o1] = a
      assert.deepEqual o1, value: 2 # oh...
    o = {}
    o.value = 1
    subjectX.onNext o
    o.value = 2
    subjectX.onNext o
    subjectX.onCompleted()

  it 'key selector', ->
    hash = require 'object-hash'
    subjectX = new Rx.Subject()
    subjectX
    .distinctUntilChanged hash
    .toArray()
    .subscribe (a) ->
      assert a.length is 2
      [o1, o2] = a
      assert.deepEqual o1, value: 2 # oh...
      assert.deepEqual o2, value: 2
    o = {}
    o.value = 1
    subjectX.onNext o
    o.value = 2
    subjectX.onNext o
    subjectX.onCompleted()

原因としては currentKey として保持している直前の値はその参照を書き換えられると、比較が正しく動かないため。