function stackSet(key, value) {
	  var data = this.__data__,
	      array = data.array;

	  if (array) {
	    if (array.length < (LARGE_ARRAY_SIZE - 1)) {
	      assocSet(array, key, value);
	    } else {
	      data.array = null;
	      data.map = new MapCache(array);
	    }
	  }
	  var map = data.map;
	  if (map) {
	    map.set(key, value);
	  }
	  return this;
	}
Sets the stack `key` to `value`.

@private
@name set
@memberOf Stack
@param {string} key The key of the value to set.
@param {*} value The value to set.
@returns {Object} Returns the stack cache object.