code: function(key, value) {
          var keys = this.keys;
          var values = this.values;
          var guid = guidFor(key);
  
          // ensure we don't store -0
          var k = key === -0 ? 0 : key;
  
          keys.add(k, guid);
  
          values[guid] = value;
  
          this.size = keys.size;
  
          return this;
        }
docs: Adds a value to the map. If a value for the given key has already been
  provided, the new value will replace the old value.
  
  @method set
  @param {*} key
  @param {*} value
  @return {Ember.Map}