code: function(value, context, argCount) {
                  if (value == null) return _.identity;
                  if (_.isFunction(value)) return optimizeCb(value, context, argCount);
                  if (_.isObject(value)) return _.matcher(value);
                  return _.property(value);
                }
docs: A mostly-internal function to generate callbacks that can be applied to each element in a collection, returning the desired result — either identity, an arbitrary callback, a property matcher, or a property accessor.