Re: Arguments by reference?

[Rici Lake <lua@...>]

On 1-Sep-05, at 12:48 PM, Brent Arias wrote:

> Not passed by reference? And not passed by copy either?  I don't get 
> it.
> Those are the only two options.  If its not a reference/pointer, and 
> its not
> a copy of the value...then...what?

If you don't think of variables and instead think of values, it is 
simpler :)

Consider the primitive value 3. If (in C), I do:

  somefunc(3);

Would you say that the 3 is being "copied"? Or that somefunc just gets 
the value 3?

Now, in C++, if I call:

  somefunc(someobj);

(i.e. not a reference or pointer, but someobj itself)

someobj is definitely copied, in the sense that the copy constructor is 
invoked.

Lua doesn't do that, which is why I said that it is not passed by copy. 
So in Lua:

  somefunc(3)
  somefunc(someobj)

both do exactly the same thing: somefunc is passed the value, which is 
3 or someobj, respectively. It cannot mutate 3, so the difference is 
ignorable, but it may be able to mutate someobj (if someobj were a 
mutable object), and if it does, it is mutating the same value as was 
passed to it.