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From: bobduff@world.std.com (Robert A Duff)
Subject: Re: Garbage Collection in Ada
Date: 1996/11/06
Message-ID: <E0GHGv.17G@world.std.com>#1/1
X-Deja-AN: 194890370
references: <01bbc6a3$4cf03480$829d6482@joy.ericsson.se>
 <E055IC.26I.0.-s@inmet.camb.inmet.com>
 <mheaney-ya023280000311962335300001@news.ni.net>
organization: The World Public Access UNIX, Brookline, MA
newsgroups: comp.lang.ada
Date: 1996-11-06T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <mheaney-ya023280000311962335300001@news.ni.net>,
Matthew Heaney <mheaney@ni.net> wrote:
>Language designers: any reason why overloading "all" would be too hard?

Well, functions return values (or constant objects, if you want to be
precise in Ada 95 terms), whereas "P.all" returns a variable (if P is an
access-to-variable type).  So it wouldn't work.  C++ has references,
which are more like variables.  (By the way, I find the notation ".all"
to be rather ugly -- I prefer Pascal's "^", or even C's "*".)

I agree with your point, though.  It's not just ".all", but many
notations in Ada are predefined, so you can't make a user-defined
abstraction that "looks like" a predefined one.  For example, suppose
you want to have an associative array data type, which is just like a
normal array, except that the index type can be something like String.
You can do that, but you have to use a different notation for array
indexing, aggregates, etc.  Or, suppose you want to make a
multi-precision integer type, which is just like a normal integer,
except it won't overflow on large numbers.  Well, you can't use numeric
literals, case statements, etc.

The danger of course is that if the user defines a numeric literal to do
something weird (with side effects!), then the program is harder to
understand.  But that problem already exists in Ada for "+", for
example.  The answer is for the programmer to use good taste when
redefining "+".

- Bob