Re: Ada OS based on Minix3

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

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:14ay3vz2ngj9s.1bmilwgckl3lc$.dlg@40tude.net...
...
>>> 5. Getting a pool-specific pointer to the object upon
>>> initialization/finalization, when the object is allocated in such a 
>>> pool.
>>> (Unchecked_Conversion is really nasty there)
>>
>> I think you mean Unchecked_Access -- Unchecked_Conversion is not
>> necessary.
>>
>> I don't see how this can make sense.  In Initialize or Finalize, you
>> don't know whether the object is in a pool, nor which pool.  So how can
>> you get a pool-specific pointer?
>
> That is exactly the problem. Consider objects allocated on a user-defined
> pool. The object are linked into some list. When a new object is created
> the "constructor" places it into the list. When the object is destroyed,
> the "destructor" removes it. For both, you need a self-pointer, but you
> cannot get it from an "in out" parameter.

Sorry, but this is completely wrong. This is *exactly* how Claw works, and 
it works fine with Ada 95. It is perfectly OK to get a pointer from a 
parameter of a tagged object. You do have to use 'Unchecked_Access, but that 
is no problem if you are using Finalize to clean up.

...
>> 10. Reify the finalization operation (that is, the operation on some
>>     type that calls Finalize on all the parts of it, including the
>>     whole).
>
> I.e. a destructor. But it is semantically broken to have such. It would
> destroy an object leaving a dangling typed name of.
>
> I think that the trick can be achieved with an access type to some fake
> storage pool. The Unchecked_Deallocation is called on the pointer. That
> does the finalization. Then the pool's Deallocate is called, which does
> nothing.

Yup. And you can do that now. So what's the big deal. At worst, it's not as 
convinient as it could be.

Most of the rest of the stuff that you and Bob have talked about is too 
incompatible to consider for Ada. A new Ada-like language could do these 
things, but there isn't much likelyhood of anyone using that.

                              Randy.