transform_iterator won't work with non-const operator() call for function object

[zhuo.qiang@…]

transform_iterator declare it's copied function object as:

    UnaryFunc m_f;

And it's dereference function as:

    typename super_t::reference dereference() const
    { return m_f(*this->base()); }

which makes it impossible to cooperate with function object with non-const operator() overloading, and and it will also make transformed adaptor in boost::range not work:

struct Fun
{
    typedef bool result_type;
    
    bool operator()(int a)
    {
        return a != 1;
    }
};
    Fun f;
    boost::find(all|boost::adaptors::transformed(f), true);

A boost::ref won't work here since the result has no result_type defined

And the only solution would be using a boost::function to hold the original function object, however, doing so will give unnecessary run time cost.

I suggest change the UnaryFunc m_f; definition to mutable, so that it will work with non-const functor.

    UnaryFunc mutable m_f;

[anonymous]

Please prioritize this ticket. With C++11 mutable lambdas (for which the Standard mandates a non-const operator()) this problem becomes much more frequent.