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

From: Dan W. (danw_at_[hidden])
Date: 2004-01-08 14:17:37

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 >").

>>   (B) also as of version 1.01 private inheritance is used.
>>   (C) class invariants is templeted per derived, and therefore
>>      does not conduce to unwanted sibling relationships
>>   (D) the only virtual function inherited from invariants class
>>      is check_invariants(), which is pure virtual in the base,
>>      and no longer virtual in derived. This AFAIK should not
>>      cause the compiler to generate an otherwise absent virtual
>>      table.
>>   (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:
> 
>    struct my_type
>    {
>    private:
>        friend class invariant_access;
>        void invariant() const
>        {
>            ...
>        }
>    };
> 
> 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.