Re: Ada and Unicode

[Thomas <fantome.forums.tDeContes@free.fr.invalid>]

In article <s5k0ne$opv$1@gioia.aioe.org>,
 "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote:

> On 2021-04-19 15:15, Luke A. Guest wrote:
> > On 19/04/2021 14:10, Dmitry A. Kazakov wrote:
> > 
> >>> They're different types and should be incompatible, because, well, 
> >> they are. What does Ada have that allows for this that other languages 
> >> doesn't? Oh yeah! Types!
> >>
> >> They are subtypes, differently constrained, like Positive and Integer. 
> > 
> > No they're not. They're subtypes only and therefore compatible. The UTF 
> > string isn't constrained in any other ways.
> 
> Of course it is. There could be string encodings that have no Unicode 
> counterparts and thus missing in UTF-8/16.

1
there is missing a validity function to tell weather a given 
UTF_8_String is valid or not,
and a Dynamic_Predicate on the subtype UTF_8_String connected to the 
function.

2
more important, (when non-ASCII,) valid UTF_8_String *do not* represent 
the same thing as themselves converted to String.

> 
> >> Operations are same values are differently constrained. It does not 
> >> make sense to consider ASCII 'a', Latin-1 'a', UTF-8 'a' different. It 
> >> is same glyph differently encoded. Encoding is a representation 
> >> aspect, ergo out of the interface!

it works because 'a' is ASCII.
if you try it with a non-ASCII character, all goes wrong.

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