gamblers-dice | A terrible idea | Analytics library

What do variables/parameters hold? They hold values. What is the nature of the values they store? For Value types (struct) they store the value itself.

But for Reference types (class), they store a reference; they don't store the object itself, that's located elsewhere.

It is these that are copied-in in the default pass-by-value parameter passing in C#. And copying a reference is not the same as creating a copy of the object to which it refers. So, even without ref, you're dealing with a single object both inside and outside the method. Any changes to the object will, obviously, be visible externally.

You only need ref if a) you're going to reassign the parameter and that reassignment should be externally visible or b) you're mutating a Value type and that mutation should be externally visible.

And, in case the above isn't clear enough, I will explicitly state it here - Random is a Reference type.

Bonus reading: The Truth About Value Types by Eric Lippert, which you may not be ready for but does help dispel some common myths that you may pick up along the way.