Why is the original object changed after a copy, without using ref arguments?

Question

At work we were encountering a problem where the original object was changed after we send a copy through a method. We did find a workaround by using IClonable

Answer 1

I see two issues here...

Making a Copy of an object

var copy = myClass; does not make a copy - what it really does is create a second reference ("pointer") to myClass (naming the variable "copy" is misleading). So you have myClass and copy pointing to the same exact object.

To make a copy you have to do something like:

var copy = new MyClass(myClass);

Notice that I created a new object.

Passing By Reference

1. When passing value type variables without ref, the variable cannot be changed by the the receiving method.

   Example: DoSomething(int foo) - DoSomething cannot affect the value of foo outside of itself.

2. When passing value type variables with ref, the variable can be changed

   Example: DoSomething(ref int foo) - if DoSomething changes foo, it will remain changed.

3. When passing an object without ref, the object's data can be changed, but the reference to the object cannot be changed.

void DoSomething(MyClass myClass)
{
    myClass.myString = "ABC"   // the string is set to ABC
    myClass = new MyClass();   // has no affect - or may not even be allowed
}

4. When passing an object with ref, the object's data can be changed, and the reference to the object can be changed.

void DoSomething(ref MyClass myClass)
{
    myClass.myString = "ABC"   // the string is set to ABC
    myClass = new MyClass();   // the string will now be "" since myClass has been changed
}