c# - Generic method multiple (OR) type constraint

Question

Reading this, I learned it was possible to allow a method to accept parameters of multiple types by making it a generic method. In the example, the following code is used with a type constraint to ensure "U" is an IEnumerable<T>.

public T DoSomething<U, T>(U arg) where U : IEnumerable<T>
{
    return arg.First();
}

I found some more code which allowed adding multiple type constraints, such as:

public void test<T>(string a, T arg) where T: ParentClass, ChildClass 
{
    //do something
}

However, this code appears to enforce that arg must be both a type of ParentClass and ChildClass. What I want to do is say that arg could be a type of ParentClass or ChildClass in the following manner:

public void test<T>(string a, T arg) where T: string OR Exception
{
//do something
}

Your help is appreciated as always!

Answer 1

That is not possible. You can, however, define overloads for specific types:

public void test(string a, string arg);
public void test(string a, Exception arg);

If those are part of a generic class, they will be preferred over the generic version of the method.