Re: Depending on passing mechanism

[dewar@merv.cs.nyu.edu (Robert Dewar)]

1.  _Always_ pass by reference.  This can be forced in C/C++ by certain
coding styles.  Any aliasing is assumed to be programmer-intended, and
has a relatively simple programming model.  (You may have to liberally
sprinkle 'volatile'-type thingy's around as well.)  There is a certain
cost, but on modern microprocessors the cost is not exorbitant, and certainly
less than the cost of a 777.

  This is VERY difficult in distributed environments where there is no
  shared memory between caller and callee, and prohibitively expensive.
  (The 777 rhetoric hardly impresses us with the validity of your
  arguments)

  It is of course possible to force this same effect in Ada 95, by the
  use of access parameters.

2.  _Always_ pass by value.  This is really possible only in a 100%
functional language like Haskell.

  Nonsense, it is always possible to pass by value, I have no idea what
  Henry is talking about when he says this. Certainly not Ada. The penalty
  for passing by value is simply the cost of copying (once for in
  parameters, twice for in out), but these copies can be prohibitively
  expensive for large arrays.

3.  Add a new concept to your language: 'linear'/'unique' types.  These
objects are guaranteed to be singly referenced because this is enforced
by the type system.  Poof!  No aliasing!  This concept was pioneered by
NIL/Hermes, and has recently been incorporated into some logical (prolog-like)
languages and some functional languages ('Clean' from KU Leaven).  There is a
large and growing body of mathematics called 'linear logic' that puts linear
types on a firm theoretical foundation.

  Pretty much irrelevant theoretical nonsense with respect to the specific
  issue at hand, but this and to some extent the previous two responses
  tend to suggest a rather irrelevant approach that is not grounded in
  the specific Ada question at hand.

The NIL/Hermes people tried to get people in the Ada community to pay
attention, but they were completely ignored, and Ada95 suffered for it.

  Complete nonsense

One has to wonder if Henry knows Ada when he writes this?