How to specify a List<MyCustomType> as a "Return Type" for a UML Interface Property

Question

In my Visio 2007 UML document I am unable to figure out how I can add an operation to an Interface that returns a generic List<MyCustomType> type.

For example:

Say I have a class named "MyClass" and an Interface named "IFace". IFace has a signature of a method that returns a Generic List of MyClass.

For clarity, here's an example of the C# code:

namespace StackO
{
    public interface IFace
    {
        List<MyClass> SomeMethod(string data);    
    }

    public class MyClass
    {
    }
}

Here's a screenshot of where I'm stuck:

It seems as though the only way to specify a List<MyClass> as my Return Type is to create another user-defined datatype that is explicitly written as List<MyClass>. If this is the case, so be it. However, I'm posting this in hopes that there is a better/proper way to do this.

How can I define the Return Type of an Operation of a Visio Interface to be a Generic List of a User-Defined Datatype?

Answer 1

In the Class diagram properties > Go to operations > select the return type you are interested in changing and click properties.

In the next dialog you will have option for setting prefix List< and suffix >.

This way you can specify the return type as List<>.

I see this option in Visio 2010. But I am not sure if this option is available in Visio 2007.

Answer 2

There is no such a thing as T1<T2> in UML class diagrams.

If you want to specify that the method returns several values, the correct notation is:

SomeMethod(data: String) : MyClass [*]

This notation is much more powerful than the one used by C#. List<MyClass> SomeMethod(string data) gives no information about the contract of the method. With UML, you know that in:

SomeMethod(data: String) : MyClass [*]
SomethingElse() : String [1..*]
LastExample(number: UnlimitedNatural) : Integer [0..1]

SomeMethod returns a sequence containing zero or more elements. SomethingElse returns a sequence of one or several elements: this sequence is never empty. Finally, LastExample returns an optional value. This could be expressed in C# as int? LastExample(uint number) — see, no IEnumerable here.

Also note that:

SomeMethod(data: String) : MyClass [0..*]

shouldn't be used, since [*] means the same thing and is shorter. As for:

SomeMethod(data: String) : MyClass [0..n]

is incorrect, despite being used a lot on the internet.