On Fri, Apr 30, 2010 at 3:37 AM, Samuel Debionne <debionne@hydrowide.com> 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