[boost] Re: Iterator adaptors <-> boost::bind interaction

From: David Abrahams (dave_at_[hidden])
Date: 2005-05-24 19:39:52

Aleksey Gurtovoy <agurtovoy_at_[hidden]> writes:

>> Maybe you could add some commentary?
>
> Sure. Both of the marked lines above invoke undefined behavior on
> dereference of the corresponding composite transform iterator because
> its 'operator*' by the iterator is basically equivalent to this:
>
>        int const& operator*() const
>     // ^^^^^^^^^^
>       {
>           // returning a reference to a member of a temporary object 
>           // that will be destroyed at the end of the function block scope
>           return make_x( *base() ).get_i(); // #1
>     //    return X( base()->x ).get_i(); // #2
>       }

Oh.  Well, I'm not sure that separating transform_iterator and
projection_iterator would help here.  AFAICT this issue only really
applies when using make_transform_iterator, and only when you're

 a. assuming a transform_iterator always returns by value 

and

 b. unclear on what your functions are doing.

OR

 c. You expect transform_iterator to be a perfect drop-in replacement
    for the transform_iterator from the earlier Boost library, which I
    admit is a fair expectation.
    
Maybe we need a make_transform_iterator variant that allows us to
force a by-value return or something?

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com