Re: array from static predicate on enumerated type

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

On 2021-03-13 03:06, Matt Borchers wrote:
> I pretty much agree with Dmitry on this.  The usefulness of this is very, very low without better support from the language itself.  However, Dmitry, if programmers should not consider a feature of a language as an option for a solution, then it begs the question on the quality of the language, quality of the compiler, or questions the abilities of caretakers of Ada.  Don't get me wrong, however, I think Ada is exceptional.

Subtyping is a very difficult problem. When a new type is created by 
constraining [*] this necessarily breaks things.

Ada 83 was very careful to limit that to ranges and discriminant values. 
That breaks, sure, but the damage is minor and can be controlled [by the 
programmer]. In contrast, an arbitrary constraint [as well as arbitrary 
extension] is like a carpet bombing.

My view, as a programmer, is that features of type algebra [which 
subtyping by constraining is] must be carefully limited to enable 
massive language support in detection of substitutablity issues at 
*compile* time. Features must be reasonably safe to use.

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*  Sorry, guys, Ada subtypes are types.

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