Re: Arguments by reference?

[Glenn Maynard <glenn@...>]

On Thu, Sep 01, 2005 at 10:48:11AM -0700, Brent Arias wrote:
> Wow! Now this is bewildering:
> 
> ------------------
> They might look like they're being passed by reference, but they're
> not. All arguments in Lua are passed by value. They are not passed by
> copy, so when you pass a table (by value) you are passed the same
> table,
> ------------------
> 
> 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?
> 
> Perhaps this is just a semantics issue.  Perhaps a variable "containing" a
> table, internally is implemented somewhat like a pointer, but is exposed to
> lua as a regular variable.  If that is the case (and I suppose that is
> correct), then you could say tables are passed by value, yet modifying the
> content of the passed table will indeed affect the original (as if it were a
> pass by reference).

At least by my notion of semantics, all variables are passed by copy, as in
C.  The pointer comparison is accurate:

 void foo( int *p ) { p[0] = 1; p = NULL; } // C
 function foo( p ) p[0] = 1; p = nil; end   -- Lua 

are similar in behavior.  These pass by copy, but it's a shallow copy, not
a deep copy.

-- 
Glenn Maynard