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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: gnat.string_split , howto manipulate slice numbers
Date: Wed, 30 Oct 2019 11:30:55 +0000
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Date: 2019-10-30T11:30:55+00:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> On 2019-10-29 19:33, J-P. Rosen wrote:
>> Le 29/10/2019 à 17:47, Simon Wright a écrit :
>>>     type Slice_Number is new Natural;
>>>
>>> For me, this carries declaring a type rather than a subtype further than
>>> necessary. A subtype? Or why not just use Natural?
>> Integer (or its subtypes) should be avoided in general. It is non
>> portable, and carries no information to the reader about the purpose of
>> the type. Making appropriate types that cannot be mixed is key to the
>> philosophy of Ada ("strong typing", you know...).
>
> Another reason is to distinguish index/key from position. When both
> are subtypes of integer some bugs may slip through, e.g.
>
>    A (A'Length - 1)
>
> This is broken code, but the compiler cannot detect it.

How is it broken?

> Or when you instantiate a generic container:
>
> generic
>    type Position_Type is range <>;
>    type Index_Type is private;
>    type Element_Type is private;
> package Generic_Container is
>    ...
>    function Get (Container : Container_Type; Position : Position_Type)
>       return Element_Type;
>    function Get (Container : Container_Type; Key : Key_Type)
>       return Element_Type;
>
> It fails when instantiated with subtypes of same integer type.

Again.You'd need to use named parameter association, but otherwise, what
am I missing?