Object as function argument

[Max Klyga via Digitalmars-d-learn]

On 2015-03-05 19:35:34 +0000, Chris Sperandio said:

> Hi,
> 
> I'm a developer coming from C and I've a question about class instance 
> as method or function parameter.
> In the book "The D Programming Language", I read the instance was 
> passed by reference to functions (in the opposite of structures). I 
> understood that it was the same object in the function and the caller. 
> But I'm think, I was wrong because when I print the addresses of an 
> object before the function call and inside the function, they're not 
> the same but the changes from the function are kept in the instance.
> If I use the "ref" qualifier in the function declaration, the 2 
> addresses are the same.
> 
> How do the changes work in the function? Is there a copy ? Or a "magic" 
> trick :) ?
> 
> Chris

When you write `auto myObject = new MyObject();`
`myObject` is actually a pointer to object in GC memory. Its roughly 
equivalent to `struct MyObject *myobject` in C. So when you take a 
pointer you actually take a pointer to reference on the stack and thats 
why its different in the function - variable is higher up the stack.
`ref` qualifyer guaranties that you get the pointer to the same reference.

If you really need the actual pointer to object data you can use 
`*cast(void**)&myObject`. Compiler cannot cast object reference to 
`void*` but we can trick it ;)