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Date: Mon, 22 Aug 2005 08:28:43 -0500
From: "Marc A. Criley" <mcNOSPAM@mckae.com>
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Subject: Re: basic ada question
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Date: 2005-08-22T08:28:43-05:00
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Simon Wright wrote:

> I sometimes find myself using a mixed style,
> 
>                Invalidate (Current_Item (Using),
>                            If_For_Instance =>
>                              Instance_Base_P (For_The_Instance));

I find the mixed style particularly valuable in situations where Boolean 
arguments are used.  For example, if I had the procedure declaration:

   procedure Do_Something(To_This_Instance   : in Item_Type;
                          First_Time_Through : in Boolean);

Invocations of this procedure could look like:

    Do_Something(Current_Instance, True);

Correct, but that "True" doesn't tell you a whole lot.  You could
define your own two-value enumeration, with enumerals First and
Not_First, but all you really need in that procedure is just plain
old Boolean.  You could also subtype Boolean, use renames clauses on,
or define constants for, True and False, but that's just more code
that could easily distract the reader, when all you really need is
an invocation like this:

    Do_Something(Current_Instance, First_Time_Through => True);

Within the procedure's implementation, the context and appropriateness
of the Boolean argument is apparent, and the invocation of it using
named notation for the Boolean parameter pulls some of that context into
the caller for increased clarity.

-- Marc A. Criley
-- McKae Technologies
-- www.mckae.com
-- DTraq - XPath In Ada - XML EZ Out