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From: "Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org>
Newsgroups: comp.lang.ada
Subject: Re: Ada.Strings.Unbounded vs Ada.Containers.Indefinite_Holders
Date: Sat, 23 Sep 2017 11:16:59 +0200
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Date: 2017-09-23T11:16:59+02:00
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On 09/23/2017 10:09 AM, Dmitry A. Kazakov wrote:
> On 2017-09-23 00:15, Victor Porton wrote:
>>
>> In my opinion, it would be better to change RM phrasing from "null string"
>> to "empty string", because in some other languages (notably C) NULL means
>> something other. It is just confusing.
> 
> The adjective null and the noun null are distinct parts of speech. C's noun null 
> is an abbreviation of null pointer. If pointers can be null so strings can.

Another way to look at it: Ada has the formal concepts of:

* null access value ARM 4.2(9)
* null array 3.6.1(7)
* null constraint 3.2(7/2)
* null_exclusion 3.10(5.1/2)
* null extension 3.9.1(4.1/2)
* null procedure 6.7(3/3)
* null range 3.5(4)
* null record 3.8(15)
* null slice 4.1.2(7)
* null string literal 2.6(6)
* null value (of an access type) 3.10(13/2)
* null_statement 5.1(6)

not to mention the language-defined identifiers

Null_Address
    in System   13.7(12)
Null_Bounded_String
    in Ada.Strings.Bounded   A.4.4(7)
Null_Id
    in Ada.Exceptions   11.4.1(2/2)
Null_Occurrence
    in Ada.Exceptions   11.4.1(3/2)
Null_Ptr
    in Interfaces.C.Strings   B.3.1(7)
Null_Set
    in Ada.Strings.Maps   A.4.2(5)
    in Ada.Strings.Wide_Maps   A.4.7(5)
    in Ada.Strings.Wide_Wide_Maps   A.4.8(5/2)
Null_Task_Id
    in Ada.Task_Identification   C.7.1(2/2)
Null_Unbounded_String
    in Ada.Strings.Unbounded   A.4.5(5)

(Just look under N in the index.)

It's called overloading. Many of these cases refer to things that can have 
components and mean one with zero components: a null record has no components, a 
null array has no components ('Length = 0), a null string literal has no 
characters, a null set has no members, ... It should not be confusing.

-- 
Jeff Carter
"You cheesy lot of second-hand electric donkey-bottom biters."
Monty Python & the Holy Grail
14