Re: [boost] Re: "invariants" class; Version 1.01

From: Daniel Wallin (dalwan01_at_[hidden])
Date: 2004-01-08 19:29:08

Dan W. wrote:
> Daniel Wallin wrote:
> 
>> Dan W. wrote:
>>
>>>   It's been suggested to me that introducing inheritance and
>>>   virtual functions via inheritance in debug mode might not be
>>>   good ideas. Note however that,
>>>   (A) as of version 1.01 there is no longer size augmentation
>>>      via inheritance, since the only data member was removed.
>>
>>
>> Yes there is, there's still a virtual member function.
> 
> 
> I meant no "size augmentation" in the sense of sizeof(a_class) being 
> different from sizeof("a_class : invariants< a_class >").

If sizeof("a_class : invariants< a_class >") means sizeof(a_class when
derived from invariants<a_class>) then yes, the size still differs
because of the virtual function.

>>> <snip>
>>>   (E) Using inheritance allows one to use succint class member
>>>      names in the invariant assertions, rather than have to
>>>      dereference a pointer, or reference via '.'.
>>
>>
>>  From my implementation:
>>
>> <snip>
>> I don't see how it's related to inheritance. Or did you mean something
>> else?
> 
> 
> I must have meant something else, since I don't understand what you're 
> trying to tell me.
> What I say in (E), if that's what you're not sure what I mean, is that if
> 
> class my_class
> {
>    int a, b, c;
>    struct check_invariants
>    {
>       void check( my_class const & );
>    };
>    friend class check_invariants;
> };
> 
> then I need to de-reference members when writing assertions...
> 
> void my_class::check_invariants::check( my_class const & _ )
> {
>    assert( _.a + _.b == _.c );
> }
> 
> I find it more intuitive for check() to be a member function.

Again, this has nothing to do with inheritance. check_invariants() can
be a member function regardless if my_class is derived from invariants<>
or not. Like this in the code I posted:

   class my_class
   {
       int a, b, c;
       friend class invariant_access;

       void invariant() const
       {
           assert(a + b == c);
       }
   };

-- 
Daniel Wallin