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From: "Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org>
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Subject: Re: How can I create an empty array of a generic type?
Date: Sun, 14 Jul 2019 13:27:54 +0200
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Date: 2019-07-14T13:27:54+02:00
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On 7/14/19 1:15 PM, reinert wrote:
> lørdag 13. juli 2019 07.24.10 UTC+2 skrev J-P. Rosen følgende:
> .....
>> You can avoid it:
>>     Empty_Key  : constant Key_Type(1..0) := (others => <>);
>>
> 
> But Key_Type is an array indexed by Positive (> 0).
> The zero in "Key_Type(1..0)" is not so intuitive for me (outside the range) ?

Try this:

with Ada.Text_IO;

procedure Null_Last is
    S : constant String := "";
begin -- Null_Last
    Ada.Text_IO.Put_Line (Item => Integer'Image (S'Last) );
end Null_Last;

See also ARM 3.5:

(4) "A range with lower bound L and upper bound R is described by “L .. R”. If R 
is less than L, then the range is a null range, and specifies an empty set of 
values."

(8) "A range is compatible with a scalar subtype if and only if it is either a 
null range or each bound of the range belongs to the range of the subtype."

So 1 .. 0 is a null range. A null range is compatible with any scalar subtype, 
so it is compatible with Positive.

-- 
Jeff Carter
"I have a very small head and I had
better learn to live with it ..."
Edsger Dijkstra
158