Re: Anonymous Access and Accessibility Levels

[Jere <jhb.chat@gmail.com>]

On Friday, April 26, 2019 at 1:12:43 PM UTC-4, G.B. wrote:
> On 24.04.19 12:42, Jere wrote:
> 
> > I'm definitely aware of the HoD and its reputation.  I am a bit
> > discourage that there is not any resource (person or written)
> > available to help newcomers (or heck even somewhat experienced
> > Ada programmers) with issues like these.
> 
> It might be too late when designs involving anonymous access
> types become issues, but then any design can possibly
> have fewer issues if the Ada Rationale is first consulted.
> I'm concluding this in part observing designs of programmers who
> have chosen to transport a pointer-based mind set to Ada.
> This means, they are perhaps not aware of the Rationale.
> 
> As an additional consequence, if GNAT advises to use pointer
> types, programmers may not always be given the best advice
> from a design point of view, only from a compiler that cannot
> undo designs.

I'm not sure the Rationale covers all of the use cases where 
access types end up being needed.  I know working in a lot of
non heap based designs (no heap on my chip), General access types
occasionally have to be used as part of the innards of some 
complex type.  Named access types are too restrictive and end up
requiring the use of Unchecked_Access and in some other cases can 
lead to bad designs when used.  That leaves anonymous access types, 
which seem incomplete.  Ada needs safe access types that are 
more flexible than named access types.  They don't have to be 
anonymous necessarily, but they are a gap in the language design,
especially when you are dealing with limited types, which have 
no container support or similar, so the standard ways of avoiding
access types don't apply.