Re: Preventing type extensions

[Ludovic Brenta <ludovic@ludovic-brenta.org>]

Florian Weimer writes on comp.lang.ada:
> * Ludovic Brenta:
>
>> Another area where Ada helps certification is where it distinguishes
>> pool-specific from general access types.  C and C++ are both completely
>> helpless in this respect.  Consider:
>>
>> type T_Access is access T'Class; -- no equivalent in C++
>> type T_General_Access is access all T'Class; -- equivalent to T* in C++
>
> Iterators are examples of pool-specific allocators in C++.

How so?  IIUC, iterators are not even a language construct, only an
idiom in the standard library.

> It's also common to define your own pointer types in C++.

Do you mean that

typedef T* T_Pointer;

is common?

> It's hard to beat the C++ type system in terms of expressiveness.

I disagree; I just showed the opposite in my previous post.  C++ does
not have specific pointer types, for example; only class-wide ones.

>> Hey, just a wild idea: how about
>>
>> type T_Stack_Access is access aliased T;
>>
>> which indicates that access values of this type can *only* designate
>> aliased objects that are on the stack, and never on the heap?
>
> I don't think this would provide useful information.  Tasks blur the
> boundary between heap and stack allocation.

Insofar as each new task creates a stack from the heap of the
environment task, yes.  But the Ravenscar profile forbids this, so the
"access aliased" feature might be useful in this context, which happens
to be the context where certification is needed.

-- 
Ludovic Brenta.