Re: Parameterised 'Image Attributes

["Randy Brukardt" <randy@rrsoftware.com>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:uchukd$1lnvp$1@dont-email.me...
> On 2023-08-28 11:18, Stephen Davies wrote:
>
...
>Neither there is one why 'Image must be a non-overridable attribute

There actually is a good reason for this. Attributes have global visibility. 
So if you allowed overriding of attributes, then a with added or removed in 
a remote part of a program could silently change the behavior of code that 
has no knowledge of of the change. That would be bad for "programming in the 
large". Note that Ada 95 was proven to have no such cases, and we've tried 
very hard to avoid them.

One could imagine adding rather severe restrictions to overriding of 
attributes to eliminate this problem (for instance, only allowing it for 
primitive operations of the type), but that would eliminate all real value 
of the feature (you can always use a primitive function and "use all" to get 
the same effect without any new features).

For 'Image specifically, the design of the attribute doesn't work well for 
composition (for Image for composite types), which is why Ada 2022 has a 
separate attribute that can be overridden similar to a stream attribute.

                          Randy.