Re: Call by reference vs. call by value

[ok@goanna.cs.rmit.edu.au (Richard A. O'Keefe)]

bobduff@world.std.com (Robert A Duff) writes:

>Yes, that's one reasonable solution.  It shouldn't be a pragma, but
>should use some sensible syntax.  Some Pascal compilers do something
>like this -- there are by-value parameters, and CONST parameters (which
>are by-reference, but still in-mode), and VAR parameters (which are
>by-ref/in-out).  Maybe CONST parameters are part of standard Pascal now;
>I don't know.  Anyway, this solution has some problems (passing of
>components of packed things, forcing the programmer to specify something
>that *usually* doesn't matter, ..)

In ISO 10206 (ISO Pascal Extended) there are

              x: T;   -- by value, local copy modifiable
          var x: T;   -- by reference, original modifiable
protected     x: T;   -- as if by value, local copy not modifiable
protected var x: T;   -- as if by reference, original not modifiable

'out' or 'in out' would have to be implemented as 'var', which specifies
by-reference.  'in' corresponds to either protected value or protected var,
both of which are more specific than in Ada.  I am somewhat surprised that
they didn't include protected pointers.

-- 
Fifty years of programming language research, and we end up with C++ ???
Richard A. O'Keefe; http://www.cs.rmit.edu.au/~ok; RMIT Comp.Sci.