I decided to make it to expect one single object with those data pieces as its arguments, like:
The more proper term would be object constructor; this may also give you a better idea of what you are actually trying to do.
Now the parameter provided to the constructor is some anonymous class that understands
arg_2. UML models this via
DataTypes, denoted with the
A DataType is a kind of Classifier. DataType differs from Class in that instances of a DataType are identified only by their value. All instances of a DataType with the same value are considered to be equal instances. [UML Spec 10.2]
So for example your case could be modeled as the following: