Re: Your June 7 change to expand_expr

[Mark Mitchell <mark at markmitchell dot com>]

>>>>> "Richard" == Richard Kenner <kenner@vlsi1.ultra.nyu.edu> writes:

    Jim>     In C++, a REFERENCE_TYPE points at an object.  In
    Jim> Ada, a REFERENCE_TYPE points into an object.

    Richard> No.  In Ada it's like a C pointer: it *can* point into an
    Richard> object, but usually points at an object.

I'm not sure I know quite what you two mean by these words, but here's
my take, as one knowledgeable about C++:

A C++ reference type is precisely like a C pointer type, with a few
variations:

  o References can never be NULL.
  o References must be initialized and cannot be modified.
    (You can modify the thing referred to, but cannot modify 
     which thing the reference refers to.)
  o Similarly, you cannot take the address of a reference.
  o You don't have to write (*r) to derefernce a reference,
    and you write r. rather than r-> to use a reference to 
    a structure.

Other than that, there's no real difference.  In particular, given
something like:

  struct S {
    int i;
  } s;

which means in C++ just what it means in C, you can have:

  struct S& sr = s; /* sr is a reference to s.  */
  int&      ir = s.i; /* ir is a reference to s.i.  */

So, I don't see a problem with Kenner using references in Ada.  It
would be nice if references are always non-NULL in Ada, but I don't
think GCC yet makes use of this information in any way.  Kenner is
correct; if we wish to mandate that any of the C++ reference
properties always hold for REFERENCE_TYPEs we should document that
clearly. 

-- 
Mark Mitchell 			mark@markmitchell.com
Mark Mitchell Consulting	http://www.markmitchell.com