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From: Victor Porton <porton@narod.ru>
Newsgroups: comp.lang.ada
Subject: Re: Ada.Strings.Unbounded vs Ada.Containers.Indefinite_Holders
Date: Fri, 22 Sep 2017 15:16:54 +0300
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Date: 2017-09-22T15:16:54+03:00
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AdaMagica wrote:

> Am Donnerstag, 21. September 2017 20:14:29 UTC+2 schrieb Victor Porton:
>> This may be a little slower.
> 
> Why do you care for performance? Have you ever measured what you are
> worrying about?
> 
> Premature optimization is the source of all evil - you can hear this
> mantra very often here.
> 
> 
>> Hm well, do I understand Null_Unbounded_String correctly? Is
>> Null_Unbounded_String really "no string"? or is it just empty string
>> ("")?
> 
> It's the latter. Is RM A.4.5(73) and 2.5(6) clear enough?

The problem I asked about is exactly that A.4.5(73) is not clear enough. 
What is 2.5(6)? There is no (6) in RM 2.5.

Well, you are right (assuming that GCC 7.2.0 does the right thing), as this 
prints "True":

with Ada.Strings.Unbounded; use Ada.Strings.Unbounded;
with Ada.Text_IO;

procedure Test is
begin
  Ada.Text_IO.Put_Line(Boolean'Image(To_Unbounded_String("") = 
Null_Unbounded_String));
end;


-- 
Victor Porton - http://portonvictor.org