Re: Why no Ada.Wide_Directories?

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Sat, 15 Oct 2011 09:12:39 -0400, Peter C. Chapin wrote:

> On 2011-10-15 04:38, Dmitry A. Kazakov wrote:
> 
>> There are two problems with the standard:
>>
>> 1. It does not define strings and characters in terms of a code point type
>> to be consistent with Unicode;
>>
>> 2. It does not provide automatic conversions between character/string
>> types, because of the problem #1, and because the Ada type system is too
>> weak for that.
>>
>> Clearly file operations, directory operations, character maps should be
>> defined using code points rather than characters. There should be only one
>> instance of each operation/package independent on the encoding and the
>> combinations of encodings.
> 
> Disclaimer: I haven't thought about this very much.
> 
> It seems like you are expecting too much from the standard. If a 
> standard program writes files with names that the standard understands 
> then a standard program can read those files back and manipulate them 
> via Ada.Directories. Yes?

Maybe, it is difficult to guess.

Anyway, what you say is a much bigger expectation than mine. I wished mere
consistency of Ada string types with Unicode (after all Ada adopted
Unicode), which is all internal language matter. What you are expecting is
certain behavior of the language environment, which Ada cannot control at
all.

> The problem arises when you try to ask a standard program to delve into 
> system specific details such as reading arbitrary ("exotic") file names 
> supported by the system.

There is no such thing. Unicode was introduced in order to support any
thinkable names.

> C avoids this complexity by just not including directory manipulation in 
> the standard at all. Ada at least allows a standard program to 
> manipulate directories containing files written by another standard program.

As a matter of fact, it does not. Consider an Ada program creating a file
in its current directory. Let the directory path contain Unicode characters
outside Latin-1. Then another Ada program running in a different directory
won't be able to find this file. In fact you cannot even walk the file
system tree/forest using Ada.Directories. You cannot do this neither
portably, nor even system-dependent.

And it is just silly to make the point that Ada programs should read/write
only files created by other Ada programs [compiled by the same compiler, I
guess]. However even this is not guaranteed.

> I can understand that it might be nice to extend the standard to include 
> proper support for Unicode file names and such.

Ada is Unicode.

> But I don't think the 
> lack of that support can be interpreted as some kind of failure of the 
> standard.

Maybe it was a success, but some people really wished Ada.Directory be
usable for developing portable GUI programs. Presently I am using GIO
instead of Ada.Directory, and it does not make me happy.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de