cp-set

cp.js

App.Person = Ember.Object.extend({
  firstName: null,
  lastName: null,
  fullName: function(key, value, oldValue) {
    // setter
    if (arguments.length > 1) {
      var nameParts = fullNameString.split(/\s+/);
      this.set('firstName', nameParts[0]);
      this.set('lastName',  nameParts[1]);
    }

    // getter
    return this.get('firstName') + ' ' + this.get('lastName');
  }.property('firstName', 'lastName')
});

var ironMan = Person.create({
  firstName: "Tony",
  lastName:  "Stark"
});

ironMan.get('fullName'); // Tony Stark

ironMan.set('fullName', "William Burnside");
ironMan.get('fullName'); // William Burnside