Re: Preventing Unchecked_Deallocation?

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

"Maciej Sobczak" <see.my.homepage@gmail.com> wrote in message 
news:5d25ffd0-a73e-48c6-aac1-d5e3b00c4e0a@l1g2000vbc.googlegroups.com...
> On 9 Lut, 03:57, "Randy Brukardt" <ra...@rrsoftware.com> wrote:
>
>> > The smart user will define his own access types and will make pointers
>> > from your objects at the nearest opportunity and there's lots of them
>> > if the type in question is, for example, tagged.
>>
>> There is absolutely no *requirement* to use access types with tagged 
>> types.
>
> Tagged types are aliased, which allows to obtain access values from
> their objects, now there is only one step to
> Unchecked_Deallocation. :-)
>
> And this is what I had in mind - it is not possible to completely
> defend against stupidity and if the user really wants, he will
> deallocate his own pointers to your own objects, even if you have no
> access types in your package specs.
>
> Putting it in other words: make something idiot proof and somebody
> will invent better idiots.

Well, as I said, a library needs to expect the objects it exports to 
disappear at any time. If that's done (often that means the objects have to 
be controlled, so they can be removed from internal data structures before 
they're gone), then the client can deallocate to their heart's content 
without damaging the the library. (Remember, Ada finalizes when 
Unchecked_Deallocation is called. Same if you use the new subpool 
mechanisms, or containers, or static allocation.)

We took this approach in Claw, simply because I didn't relish having to 
explain to users that their "bug" was caused by their misuse of the library. 
So we tried to "idiot-proof" it as much as possible.

You're of course right that there always is a bigger idiot out there, but 
nothing semi-reasonable should be crashing reusable libraries. (One-time use 
things is a different story, but be careful - a lot of one-time use things 
tend to stick around for a long time.)

                                                         Randy.