Re: [boost] [interprocess] basic_multiallocation_iterator, operator * and -> question

From: Ion Gaztañaga (igaztanaga_at_[hidden])
Date: 2007-10-23 11:56:26

Markus Schöpflin escribió:
> Hello,
> 
> in the file mem_algo_common.hpp there is a class 
> basic_multiallocation_iterator (line 50ff).
> 
> This class contains both definitions for operator* and operator->, where 
> operator* is implemented as:
> 
>     value_type operator*() const
>     {
>        value_type v = (char*)detail::get_pointer(next_alloc_.next_);
>        return v;
>     }
> 
> and operator->() as:
> 
>     pointer operator->() const
>     { return &operator*(); }
> 
> The second definition confuses both me and my compiler. Does &operator*() 
> actually mean &(*this)? If yes, wouldn't this mean that operator-> returns 
> the address of a stack allocated result variable, namely the address of the 
> result of operator*? If no, what does this actually mean?

You are right. I'm returning the address of a temporary! I think 
conceptually the iterator is wrong. I should return char & for 
operator*() instead of char *. char *should be returned by operator->.

However this makes the code uglier:

multiallocation_iterator it = ...

for(...)
    //placement new
    new(&*it++) T();

instead of

for(...)
    //placement new
    new(*it++) T();

If I want basic_multiallocation_iterator to be a well-formed iterator I 
need to define operator->() so I think I'll need to change the interface 
of this class (I doubt anyone is using it). Give me some time to change 
it and pass the tests again.

Regards,

Ion