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.