Character'First, ASCII.NUL and others (Was: Re: TCP/IP Sockets with GNAT.Sockets)

[Adrien Plisson <aplisson-news@stochastique.net>]

Poul-Erik Andreasen wrote:
> When i started developing job i tried with ASCII.NUL
> things didn't work out(surely for som other reason);
> they did when i first was using character'first.
> (also surely for som other reason);
 >
> Are there any reason why ASCII.NUL should be better;

Character'First do not describe the NUL character. i mean, it is the 
NUL character, but you have to know the implementation details of type 
Character to see that it's first element is the NUL character.

ASCII.NUL states explicitly that you are using the NUL character, 
that's why its use should be better.

anyway, the package ASCII is described in ARM95 J.5, that means it is 
part of "Obsolescent Features". as said in the ARM, "Use of these 
features is not recommended in newly written programs.". so it is 
better than Character'First, but there exists a better way to write this.

the better way is the use of Ada.Characters.Latin_1, which defines a 
constant NUL describing the NUL character. unfortunately, the package 
name is long, so you may have to write a use clause or a rename.

with Ada.Text_IO,
     Ada.Characters.Latin_1;
procedure Test is
     -- see comments below
     use Ada.Characters.Latin_1;
     package ASCII renames Ada.Characters.Latin_1;
     package Characters renames Ada.Characters.Latin_1;

begin
     Ada.Text_IO.Put( Ada.Characters.Latin_1.NUL ); -- a bit long

     Ada.Text_IO.Put( NUL ); -- a bit short, NUL what ?
                             -- NUL Character ? not sure...

     Ada.Text_IO.Put( ASCII.NUL ); -- not recommended, there is
                                   -- a risk of confusion

     Ada.Text_IO.Put( Characters.NUL ); -- this seems better !
end Test;

besides all this, when looking at Ada.Characters.Latin_1, we see that 
NUL is defined this way :

NUL : constant Character := Character'Val(0);
	
so if you just need NUL and want to avoid declarations, you may use 
Character'Val(0), which describes the NUL character better than 
Character'First.

-- 
rien