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Date: Tue, 14 Oct 2003 10:52:15 +0100
From: Stuart Palin <stuart.palin@0.0>
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Subject: Re: += in ada
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Date: 2003-10-14T10:52:15+01:00
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Regarding this vociferous debate on the matter of operators
such as ":+=" (or however you choose to denote it).

May I ask how it might be squared with the ability to
declare and rename other operator functions and using such
operators in a post-fix fashion.

In the moments of idle curiosity I have given to the matter
the only reasonable interpretation would seem to be to treat
them not as specific operators in their own right, but as a
syntactic equivalent to the use of a more basic operator.

e.g.  a :+= b;  is equivalent to a := a + b;

Then any redefinition of "+" is inherited by ":+=".  But
this does not necessarily help clarify any post-fix form of
the operator.

Treating them as operator functions in their own right seems
to create difficulties in defining a workable specification
for the function or leads to the possibility of
"interesting" expressions such as:
  a :+= ":+="(b, c);

I presume that it might be treated like any other function
(where an exception may be raised during execution) - but
that seems to lead us into one of the other arguments
debated elsewhere (should LHS be updated/unaffected if there
is an exception).

If the post-fix form (or multiple infixed operators) were
allowed, would any special precautions be needed for
"pathological" cases.  (I'm thinking of code like:

  a :+= ":+="(a, a);
)

I suppose the other option would be to treat them not as
operators but as "assignments" (and so not support renaming
on post-fix notation) - but there seems to be a tendency in
these threads to refer to them as "operators".

--
Stuart Palin