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From: =?ISO-8859-1?Q?Hibou57_=28Yannick_Duch=EAne=29?=
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Newsgroups: comp.lang.ada
Subject: Tagged type more type safe than access to subprogram ?
Date: Wed, 28 Oct 2009 00:51:19 -0700 (PDT)
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Date: 2009-10-28T00:51:19-07:00
List-Id: <comp.lang.ada>

Hello Ada Artists,

I was reading the Ada 95 Quality and Style Guide, seeking for some
inspiration about a design / style doubt.

I came into Chapter 5, =93 CHAPTER 5: Programming Practices =94,

5.3.4 Subprogram Access Types says :
> You can achieve the same effect as access-to-subprogram types for
> dynamic selection by using abstract tagged types. You declare an
> abstract type with one abstract operation and then use an
> access-to-class-wide type to get the dispatching effect. This technique
> provides greater flexibility and type safety than access-to-subprogram ty=
pes
Here : http://www.iste.uni-stuttgart.de/ps/ada-doc/style_guide/sec_5a.html#=
5.3.4

I agree about the =93 greater flexibility=94 (I've recently meet such a
case), but I do not understand the =93 and [greater] type safety =94.

If it's Ok for me to assert that tagged type is a more flexible way
than access to subprogram, I do not see a case where access to
subprogram would be less type safe than tagged type.

If there is something I do not understand, this may means I have
something to learn about it (the purpose of the question then).

Does any one know a case which match this assertion ?

Have a nice October day