Doesn’t work with list of ints either. What’s the way of using List<> types?
Do I need to create some kind of composition or dependency before I do this? Seems strange because I can add a User as an attribute without any relationship with the User class.
There isn’t really a way. Well, not directly. The UML specification doesn’t allow for X<Y> type of attributes, therefor this isn’t supported by Visual Paradigm. Always keep in mind that Visual Paradigm strictly follows the specifications as set out by the OMG group. Thing is: UML is supposed to be indifferent of programming language and this construct is directly tied into some of those, Java and C# notably but not so much for, say, PHP, Javascript and Perl (note: best guess. I don’t know these last languages inside-out so I could be making a mistake here!).
Essentially an attribute of type List is basically a “nested” array. An array of arrays so to speak. And UML does have an answer to that with multiplicity.
For example:
But do keep in mind that you’re entering some pretty complex territory here, depending on your needs of course. Still, this is how I’d approach all this.