Re: Ada Annoyances

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

"Niklas Holsti" <niklas.holsti@tidorum.invalid> wrote in message 
news:erd8jiFhsroU1@mid.individual.net...
> On 17-06-26 02:43 , Randy Brukardt wrote:
...
>>> Point (b) is more difficult and I know of no work-around that can be
>>> applied at analysis time.
>>
>> Simply banning the use of T'Class has that effect.
>
> At design and compilation time, yes, with consequent restrictions on the 
> design. But it is not a work-around that allows static analysis of 
> programs which do use T'Class.

There's no free lunch! T'Class is by definition "indefinite", since existing 
code already compiled has to be able to handle newly defined types 
(including those that don't yet exist). That's never going to allow 
conventional static analysis.

>> It's rather drastic, but
>> it eliminates all of the dynamic features. Note that this was considered
>> important enough that the standard (in Annex H) restriction No_Dispatch 
>> has
>> this effect.
>>
>> You still get the other advantages of tagged types (extension, proper
>> inheritance for private, equality, prefixed notation, etc.), and there is
>> almost no runtime penalty (or analysis problem).
>
> For the application I most have in mind (a SW component currently using 
> discriminated records to simulate tagged types) there would be no point in 
> using tagged types with the No_Dispatch restriction. The loss of 
> class-wide programming and class-wide data structures would remove almost 
> all benefits.
>
> My hope is that a Maximum_Size aspect would let one manipulate class-wide 
> objects in the same "definite" way as is possible for variant records with 
> a default discriminant value. However, it would require that the tag of an 
> object could be changed by assignment; this is perhaps too radical a 
> change in the tagged object semantics.

That seems way too drastic a change. I could imagine an aspect like the one 
you proposed to get rid of the indirection, but changing the semantics in a 
major way seems to be more than aspects are supposed to do. And changing the 
tag via assignment means having to be prepared to change finalization of 
objects after the fact as well. Ugh.

                                        Randy.