Null unbounded string

Null unbounded string

[Victor Porton]

Is Ada.Strings.Unbounded.Null_Unbounded_String an empty string or is it 
something different (like NULL char pointer in C)?

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

Re: Null unbounded string

[mockturtle]

On Saturday, August 9, 2014 5:28:49 PM UTC+2, Victor Porton wrote:
> Is Ada.Strings.Unbounded.Null_Unbounded_String an empty string or is it 
> something different (like NULL char pointer in C)?
> 

I'm not a language lawyer, but I would say that from a "conceptual" point of view is a string (e.g., you can concatenate it with other strings).  How the null string is actually implemented, I think, it is a "private" matter of the implementation that could decide to represent it as a NULL pointer.  Maybe a LL can elaborate more on this.

Re: Null unbounded string

[Jeffrey Carter]

On 08/09/2014 08:28 AM, Victor Porton wrote:
> Is Ada.Strings.Unbounded.Null_Unbounded_String an empty string or is it
> something different (like NULL char pointer in C)?

It's equivalent to an empty string. How it's implemented is unimportant.

-- 
Jeff Carter
"Insufficient laughter--that's grounds for divorce."
Play It Again, Sam
126

Re: Null unbounded string

[Victor Porton]

Jeffrey Carter wrote:

> On 08/09/2014 08:28 AM, Victor Porton wrote:
>> Is Ada.Strings.Unbounded.Null_Unbounded_String an empty string or is it
>> something different (like NULL char pointer in C)?
> 
> It's equivalent to an empty string. How it's implemented is unimportant.

But where in the ARM it's said that it is equivalent to an empty string?

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

Re: Null unbounded string

[Simon Wright]

Victor Porton <porton@narod.ru> writes:

> Jeffrey Carter wrote:
>
>> On 08/09/2014 08:28 AM, Victor Porton wrote:
>>> Is Ada.Strings.Unbounded.Null_Unbounded_String an empty string or is it
>>> something different (like NULL char pointer in C)?
>> 
>> It's equivalent to an empty string. How it's implemented is unimportant.
>
> But where in the ARM it's said that it is equivalent to an empty string?

http://www.ada-auth.org/standards/12rm/html/RM-A-4-5.html#p73

Re: Null unbounded string

[Victor Porton]

Simon Wright wrote:

> Victor Porton <porton@narod.ru> writes:
> 
>> Jeffrey Carter wrote:
>>
>>> On 08/09/2014 08:28 AM, Victor Porton wrote:
>>>> Is Ada.Strings.Unbounded.Null_Unbounded_String an empty string or is it
>>>> something different (like NULL char pointer in C)?
>>> 
>>> It's equivalent to an empty string. How it's implemented is unimportant.
>>
>> But where in the ARM it's said that it is equivalent to an empty string?
> 
> http://www.ada-auth.org/standards/12rm/html/RM-A-4-5.html#p73

It does NOT say that null string is empty string.

Should we make a formal clarification request?

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

Re: Null unbounded string

[Per Sandberg]

This is a string with "" content and you shall not reflect on the 
implementation, since this is "implementation dependent".


On 09.08.2014 17:28, Victor Porton wrote:
> Is Ada.Strings.Unbounded.Null_Unbounded_String an empty string or is it
> something different (like NULL char pointer in C)?
>

Re: Null unbounded string

[Niklas Holsti]

On 14-08-09 21:53 , Victor Porton wrote:
> Simon Wright wrote:
> 
>> Victor Porton <porton@narod.ru> writes:
>>
>>> Jeffrey Carter wrote:
>>>
>>>> On 08/09/2014 08:28 AM, Victor Porton wrote:
>>>>> Is Ada.Strings.Unbounded.Null_Unbounded_String an empty string or is it
>>>>> something different (like NULL char pointer in C)?
>>>>
>>>> It's equivalent to an empty string. How it's implemented is unimportant.
>>>
>>> But where in the ARM it's said that it is equivalent to an empty string?
>>
>> http://www.ada-auth.org/standards/12rm/html/RM-A-4-5.html#p73
> 
> It does NOT say that null string is empty string.

It says that Null_Unbounded_String represents the "null String", which
is RM-ese for a String with no elements, an empty String.

See http://www.ada-auth.org/standards/12rm/html/RM-3-6-1.html#p7 for the
definition of a "null array", and remember that String is an array type.

> Should we make a formal clarification request?

No need.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
      .      @       .

Re: Null unbounded string

[AdaMagica]

Use the top secret RM Index and you'll find 2.6(6).

Re: Null unbounded string

[Adam Beneschan]

On Saturday, August 9, 2014 1:58:10 PM UTC-7, Niklas Holsti wrote:

> > Should we make a formal clarification request?
> 
> No need.

Given that the terms are defined if you know where to look, I guess you're right that there's no *need*.  However, using the word "null" for multiple purposes (including a null access value) can be confusing, and obviously it's confused at least one person and has probably caused some confusion for others too.  So it can't hurt to suggest maybe adding a short parenthesized clarification such as "(a string with length 0)".

                                -- Adam

Re: Null unbounded string

[anon]

RM states it is a Null String

  Null_String : aliased String := "" ;

In <ls5enf$49s$1@speranza.aioe.org>, Victor Porton <porton@narod.ru> writes:
>Is Ada.Strings.Unbounded.Null_Unbounded_String an empty string or is it 
>something different (like NULL char pointer in C)?
>
>-- 
>Victor Porton - http://portonvictor.org