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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


 b. unclear on what your functions are doing.


 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

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