From: Mark Lundquist <mark@rational.com>
To: Andy Askey <ajaskey@mindspring.com>
Subject: Re: Checking Access Parameters to Procedures
Date: 2000/03/07
Date: 2000-03-07T00:00:00+00:00 [thread overview]
Message-ID: <38C56EF1.3057F00D@rational.com> (raw)
In-Reply-To: q6r8cscb2h8c9pmjhei7q1fk8hn6gimfpj@4ax.com
Andy Askey wrote:
> procedure tst_proc(this : access my_ttype'class) is
> begin
> if (this = NULL) then
> ....
> end if;
> end tst_proc;
> end tst_pkg;
>
> This does not compile so I tried every combination I can think of and
> nothing worked so far. How can I test if "this" is a NULL pointer?
The bad news: you can't.
The good news: you don't have to.
When you say "this : access my_ttype'class", you're defining an
anonymous general access-to-variable type, and anonymous access types do
not have the value Null. Null is only a value of named access types.
That's why the compiler doesn't know what you mean. At run-time, the
only way you could get a null value to try to pass in "this" would be
through an implicit type conversion from a named access type, and in
that case the conversion will raise Constraint_Error (like any other
conversion where there's no corresponding value of the target type).
prev parent reply other threads:[~2000-03-07 0:00 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2000-03-06 0:00 Checking Access Parameters to Procedures Andy Askey
2000-03-06 0:00 ` David Botton
2000-03-07 0:00 ` Mark Lundquist [this message]
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