function SetCache(values) {
	  var index = -1,
	      length = values ? values.length : 0;

	  this.__data__ = new MapCache;
	  while (++index < length) {
	    this.push(values[index]);
	  }
	}
Creates a set cache object to store unique values.

@private
@constructor
@param {Array} [values] The values to cache.