From: Georg Bauhaus <rm.plus-bug.tsoh@maps.futureapps.de>
Subject: Re: if Restrict_Func /= null confusion
Date: Sun, 30 Mar 2008 23:44:18 +0200
Date: 2008-03-30T23:44:18+02:00 [thread overview]
Message-ID: <1206913458.22025.4.camel@K72> (raw)
In-Reply-To: <95f36a62-b94c-4211-896a-300fa98932b7@x41g2000hsb.googlegroups.com> <95f36a62-b94c-4211-896a-300fa98932b7@x41g2000hsb.googlegroups.com>
On Sun, 2008-03-30 at 13:58 -0700, ma740988@gmail.com wrote:
> -- used to restrict a variable within a range
> -- for example: -PI to +PI
> type Restrict_Function is access function (X: Real4) return Real4;
>
> type Filt_Data is
> record
> Restrict_Func : Restrict_Function ;
>
> end record ;
>
>
> -- within a procedure we have
> Fdata : Filt_Data;
> Restrict_Func : Restrict_Function := FData.Restrict_Func ;
>
> if Restrict_Func /= null then
> -- stuff
> endif
>
> At issue: I'm not following the conditional logic 'if (Restrict_Func /
> = null)'. Not understanding the impetus behind the check for null.
The type Restrict_Function includes the null value.
The FData.Restrict_Func record component gets the default
initial value for access values. It is therefore null.
So Filt_Data.Restrict_Func is actually null.
prev parent reply other threads:[~2008-03-30 21:44 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-03-30 20:58 if Restrict_Func /= null confusion ma740988
2008-03-30 21:34 ` jimmaureenrogers
2008-03-30 21:36 ` Ludovic Brenta
2008-03-30 21:37 ` Robert A Duff
2008-03-30 21:44 ` Georg Bauhaus [this message]
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