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From: Robert A Duff <bobduff@TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Substrings as argument to procedures/functions
Date: Tue, 12 Apr 2016 14:17:42 -0400
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2016-04-12T14:17:42-04:00
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reinkor <reinkor@gmail.com> writes:

> I believed that if a substring is an argument to a subroutine,
> then its "range" would start at 1 (and not inherited from the calling program).
> But this seems not to be the case. 
>
> Given the following Ada source code:
>
> with Text_IO;
> use  Text_IO;
> procedure t3 is
>    package Int_Io is new Text_IO.Integer_Io (Integer);
>    use Int_Io;
>    procedure string_test1(S : String) is
>    begin
>       New_Line;
>       Put(" In string_test1: ");
>       Put(S'First,4);
>       Put(S'Last,4);
>    end string_test1;
>    Str : String := "ABCDEF";
> begin
>       string_test1(Str);
>       string_test1(Str(3..5));
> end t3;
>
> The second call to "string_test1" gives:
>
>  In string_test1:    3   5
>
> (at least on my computer).
>
> Is this correct?

Yes.

>...And in case, is it "good" ? :-)

No.  It breaks abstraction -- the procedure shouldn't have to know where
the string came from (e.g. a slice).  And it either introduces bugs
(because the code assumes S'First = 1, which is almost always true),
or it complicates the code (because you have to do arithmetic on
the bounds).

But Dmitry makes a good point.

- Bob