Re: [boost] [Bind] Interoperability of bind/mem_fn with transform_iterator

Subject: Re: [boost] [Bind] Interoperability of bind/mem_fn with transform_iterator
From: Daniel Walker (daniel.j.walker_at_[hidden])
Date: 2010-05-02 10:18:07

On Fri, Apr 30, 2010 at 3:37 AM, Samuel Debionne <debionne_at_[hidden]> wrote:
> Hello all,
> I'm scratching my head about the correct way to use transform_iterator with
> bind and mem_fn. In brief, bind and mem_fn return object functions that are
> not Default Constructible, which means that, when used to construct a
> transform_iterator, the resulting transform_iterator is not even a Trivial
> Iterator.
>
> Most of the case, it's not a problem because the transform_iterator is never
> default constructed... until some libs that do concept checking on their
> template parameters are used. See the following code for exemple :

Right, mem_fn_t is not DefaultConstructible, so a transform_iterator
with mem_fn_t does not model ForwardTraversalIterator. Likewise with
the return type of bind, which c++0x requires to be MoveConstructible
(and CopyConstructible when it's args are) but not
DefaultConstructible. In your specific example, however, you can still
build a valid ForwardTraversalIterator by using boost::function to
erase the return type of mem_fn. The same should work with bind.

 check(make_transform_iterator(
   foo_vec.begin(), function<size_t(foo&)>(mem_fn(&foo::get_id))));

 check(make_transform_iterator(
   foo_vec.begin(), function<size_t(foo&)>(mem_fn(&foo::id_))));

Daniel Walker