Re: Ada.Locales pseudo-string types

[Adam Beneschan <adam@irvine.com>]

On Tuesday, August 7, 2012 1:44:37 AM UTC-7, Marius Amado-Alves wrote:
> On Tuesday, August 7, 2012 12:07:02 AM UTC+1, Adam Beneschan wrote:
>
> What needs to change is the language doing the obvious thing: if types are compatible (down to no any level of composition) then they are convertible.
> 
> I was pretty sure arrays of convertible elements were convertible and I am much surprised to find they are not and I am still not convinced that this is not a compiler bug.

The language rule is 4.6(24.5/2): when converting between different array types, "The component subtypes shall statically match".  Statically matching subtypes means that the constraints have to be the same (and, basically, the compiler has to be able to tell at compile time that they're the same).  The rule has been there since the beginning of Ada 95; however, I believe that in Ada 83, the type conversion would have failed at runtime since the component subtypes don't have the same constraints (AI83-00022 confirms this, I think).  Thus, the language has never required a component-by-component constraint check when converting an array type.  We can argue about whether that's the right decision; but as far as I know, nobody has complained about this in 29 years [*], and most likely there has been very little need to define array-of-character types with constraints on the component subtypes, until they added these types to Ada.Locales.

So this is not a compiler bug.

[*] I don't see anything in a quick scan of the AI83's, AI95's, AI05's, or Ada Commentaries.  However, if there are other places where new feature requests can be formally made, I don't know where they are.

                            -- Adam