js/libs/ember-1.5.1.js
function ReduceComputedProperty(options) {
  var cp = this;

  this.options = options;

  this._dependentKeys = null;
  // A map of dependentKey -> [itemProperty, ...] that tracks what properties of
  // items in the array we must track to update this property.
  this._itemPropertyKeys = {};
  this._previousItemPropertyKeys = {};

  this.readOnly();
  this.cacheable();

  this.recomputeOnce = function(propertyName) {
    // What we really want to do is coalesce by <cp, propertyName>.
    // We need a form of `scheduleOnce` that accepts an arbitrary token to
    // coalesce by, in addition to the target and method.
    Ember.run.once(this, recompute, propertyName);
  };
  var recompute = function(propertyName) {
    var dependentKeys = cp._dependentKeys,
        meta = cp._instanceMeta(this, propertyName),
        callbacks = cp._callbacks();

    reset.call(this, cp, propertyName);

    meta.dependentArraysObserver.suspendArrayObservers(function () {
      forEach(cp._dependentKeys, function (dependentKey) {
        Ember.assert(
          "dependent array " + dependentKey + " must be an `Ember.Array`.  " +
          "If you are not extending arrays, you will need to wrap native arrays with `Ember.A`",
          !(Ember.isArray(get(this, dependentKey)) && !Ember.Array.detect(get(this, dependentKey))));

        if (!partiallyRecomputeFor(this, dependentKey)) { return; }

        var dependentArray = get(this, dependentKey),
            previousDependentArray = meta.dependentArrays[dependentKey];

        if (dependentArray === previousDependentArray) {
          // The array may be the same, but our item property keys may have
          // changed, so we set them up again.  We can't easily tell if they've
          // changed: the array may be the same object, but with different
          // contents.
          if (cp._previousItemPropertyKeys[dependentKey]) {
            delete cp._previousItemPropertyKeys[dependentKey];
            meta.dependentArraysObserver.setupPropertyObservers(dependentKey, cp._itemPropertyKeys[dependentKey]);
          }
        } else {
          meta.dependentArrays[dependentKey] = dependentArray;

          if (previousDependentArray) {
            meta.dependentArraysObserver.teardownObservers(previousDependentArray, dependentKey);
          }

          if (dependentArray) {
            meta.dependentArraysObserver.setupObservers(dependentArray, dependentKey);
          }
        }
      }, this);
    }, this);

    forEach(cp._dependentKeys, function(dependentKey) {
      if (!partiallyRecomputeFor(this, dependentKey)) { return; }

      var dependentArray = get(this, dependentKey);
      if (dependentArray) {
        addItems.call(this, dependentArray, callbacks, cp, propertyName, meta);
      }
    }, this);
  };


  this.func = function (propertyName) {
    Ember.assert("Computed reduce values require at least one dependent key", cp._dependentKeys);

    recompute.call(this, propertyName);

    return cp._instanceMeta(this, propertyName).getValue();
  };
}
function ReduceComputedProperty(options) {
  var cp = this;

  this.options = options;

  this._dependentKeys = null;
  // A map of dependentKey -> [itemProperty, ...] that tracks what properties of
  // items in the array we must track to update this property.
  this._itemPropertyKeys = {};
  this._previousItemPropertyKeys = {};

  this.readOnly();
  this.cacheable();

  this.recomputeOnce = function(propertyName) {
    // What we really want to do is coalesce by <cp, propertyName>.
    // We need a form of `scheduleOnce` that accepts an arbitrary token to
    // coalesce by, in addition to the target and method.
    Ember.run.once(this, recompute, propertyName);
  };
  var recompute = function(propertyName) {
    var dependentKeys = cp._dependentKeys,
        meta = cp._instanceMeta(this, propertyName),
        callbacks = cp._callbacks();

    reset.call(this, cp, propertyName);

    meta.dependentArraysObserver.suspendArrayObservers(function () {
      forEach(cp._dependentKeys, function (dependentKey) {
        Ember.assert(
          "dependent array " + dependentKey + " must be an `Ember.Array`.  " +
          "If you are not extending arrays, you will need to wrap native arrays with `Ember.A`",
          !(Ember.isArray(get(this, dependentKey)) && !Ember.Array.detect(get(this, dependentKey))));

        if (!partiallyRecomputeFor(this, dependentKey)) { return; }

        var dependentArray = get(this, dependentKey),
            previousDependentArray = meta.dependentArrays[dependentKey];

        if (dependentArray === previousDependentArray) {
          // The array may be the same, but our item property keys may have
          // changed, so we set them up again.  We can't easily tell if they've
          // changed: the array may be the same object, but with different
          // contents.
          if (cp._previousItemPropertyKeys[dependentKey]) {
            delete cp._previousItemPropertyKeys[dependentKey];
            meta.dependentArraysObserver.setupPropertyObservers(dependentKey, cp._itemPropertyKeys[dependentKey]);
          }
        } else {
          meta.dependentArrays[dependentKey] = dependentArray;

          if (previousDependentArray) {
            meta.dependentArraysObserver.teardownObservers(previousDependentArray, dependentKey);
          }

          if (dependentArray) {
            meta.dependentArraysObserver.setupObservers(dependentArray, dependentKey);
          }
        }
      }, this);
    }, this);

    forEach(cp._dependentKeys, function(dependentKey) {
      if (!partiallyRecomputeFor(this, dependentKey)) { return; }

      var dependentArray = get(this, dependentKey);
      if (dependentArray) {
        addItems.call(this, dependentArray, callbacks, cp, propertyName, meta);
      }
    }, this);
  };


  this.func = function (propertyName) {
    Ember.assert("Computed reduce values require at least one dependent key", cp._dependentKeys);

    recompute.call(this, propertyName);

    return cp._instanceMeta(this, propertyName).getValue();
  };
}
A computed property whose dependent keys are arrays and which is updated with
"one at a time" semantics.

@class ReduceComputedProperty
@namespace Ember
@extends Ember.ComputedProperty
@constructor