Re: Ada 2012 and Unicode package (UTF-nn encodings handling)

["Yannick Duchêne (Hibou57)" <yannick_duchene@yahoo.fr>]

> I still fail to see the benefit of encoding 31 bits values into 32 bits
> values...
UTF-32 is not formally an encoding format, it would better be referred to  
as a matter of Byte order. But this byte order is not system dependent, it  
is cross-platform data dependent.

> And even if implementation is not a nightmare, it always has a cost.
> Implementers are reluctant to spend money for features that nobody will
> use. (Wide_Wide_Character was forced on us by ISO).
I suppose the ISO forced the introduction of Wide_Wide_Character because  
it is part of the Unicode standard, and as you know, conformance requires  
full-conformance. There is no part-of with this, because as soon and it is  
defined, this may really have occurrences.

Imagine a web crawler: it would have to be designed with this option in  
mind. Designers could not say “We do not feel UTF-32 is useful, our  
crawler will then not be offered the capabilities of handling such  
documents”.

I just though this was a little pity, if one want to rely on the standard  
packages capabilities, then this one will only be able to do it partially.  
This would be a bit like Two way linked list without the one way (or the  
opposite). A matter of completeness.

> A package provides functionnalities. It should not presume how it is
> used. Since this package is clearly in the "string handling" class, it
> makes sense to handle this with strings.
Right, this is defined in *String*_Encoding.

> For files, the usage is to have a BOM on the first line of the file. The
> way the functions are defined makes it easy to not process the first
> line specially; see the use case in the AI.
I just had a look back at
http://www.ada-auth.org/standards/12aarm/html/AA-A-4-11.html
Only Encode has this capability (via Output_BOM : Boolean). Decode/Convert  
has nothing similar and will always skip any 16#FEFF# which will be  
interpreted as a BOM instead of as a character (there is nothing like an  
Interpret_BOM : Boolean).

But may be I am missing something. Will have a deeper look at it and at  
the AI which come with it (I saw UTF-32 was at least “pronounced” during  
the talk).