Re: Ada and Unicode

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

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.

>> 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!
> 
> As I already said in Unicode the glyph is not part part of Unicode. The 
> single code point character concept doesn't exist anymore.

It does not matter from practical point of view. Some Unicode's 
idiosyncrasies are better ignored.

>> BTW, subtype is a type.

> subtype is a compatible type.

Ada subtype is both a sub- and supertype, i.e. substitutable [or so the 
compiler thinks] in both directions. A derived tagged type is 
substitutable in only one direction.

Neither is fully "compatible", because otherwise there would be no 
reason to have an exactly same thing.

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