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From: "Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org>
Newsgroups: comp.lang.ada
Subject: Re: I'm facing an issue with: call to abstract procedure must be
 dispatching
Date: Tue, 8 Dec 2015 15:55:23 -0700
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Xref: news.eternal-september.org comp.lang.ada:28723
Date: 2015-12-08T15:55:23-07:00
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On 12/08/2015 03:43 PM, Serge Robyns wrote:
> 
> Now I've a generic question with regards to access type vs. in-out for parameters.  What is the proper Ada way to pass the "Store" around?
> Is it:
> Procedure Do_Something (A_Store : in out T_Abstract_Store'Class);
> or:
> Procedure Do_Something (A_Store : not null access T_Abstract_Store'Class);
> ?
> 
> As a former C programmer my habit goes for the not null access variant.

As an Ada S/W engineer, you should use "in out". With "in out", the compiler
does the work of passing the object in such a way that the operation can read
and modify the value. With an access, you (or whoever calls your operation) has
to do extra work to have an access value to pass. It's unnecessary extra work
and an extra chance to get something wrong, and so to be avoided.

-- 
Jeff Carter
"Your mother was a hamster and your father smelt of elderberries."
Monty Python & the Holy Grail
06