Vladimir Prus wrote:
I'm again trying to use FP in C++, and having problems. What I wanted to do was:
for_each(predecesor(v, g), /* BLL expression */ );
where predecessor(..) returns a pair of 'transform_iterator' instances. The simplest example which illustrates the problem is:
struct functor { typedef int result_type; int operator()(int i) const { return i+1; }; };
transform_iterator<functor, vector<int>::iterator> it(v.begin()); (cout << _1)(*it);
This does not compile, because operator* of transform_iterator return rvalue which can't be bound to non-const reference that operator() of the lambda expression accepts.
Of all workarounds suggsted on BLL docs, only break_const is applicable to my case (I want to pass non-const references to the lambda, so const_parameters won't do), and break_const is scary.
It looks like a serious problem with using FP, so I wonder what can be done.
How about what Peter Dimov suggested here: http://article.gmane.org/gmane.comp.lib.boost.devel/34663/match=+cref+ Something like: transform_iterator<functor, vector<int>::iterator> it(v.begin()); boost::make_adaptable<void, int>(cout << _1)(*it); -- Daniel Wallin