[Boost-users] enable_if and templated operator() of member of class template

Subject: [Boost-users] enable_if and templated operator() of member of class template
From: MM (finjulhich_at_[hidden])
Date: 2012-03-01 04:42:00

Hello,

I am using the enable_if construct to disable an operator() template member
function of a templated variant visitor:

template <typename iter_t>
class iterator_compare_visitor_ : public boost::static_visitor<bool> {
public:
  iterator_compare_visitor_(const iter_t& to_compare_to)
    : to_compare_to_(to_compare_to)
  {}

  template <typename variant_iter_t>
  typename std::enable_if< boost::mpl::contains<const_iterators_t,
iter_t>::value, bool >::type
  operator()(const variant_iter_t& it) const
  {
    return std::is_same<variant_iter_t, iter_t>::value &&
it==to_compare_to_;
  }

  template <typename variant_iter_t> 
  typename std::enable_if< boost::mpl::contains<const_reverse_iterators_t,
iter_t>::value, bool >::type 
  operator()(const variant_iter_t& it) const
  {
    return std::is_same<variant_iter_t, iter_t>::value &&
it==to_compare_to_.base();
  }

private:
  const iter_t& to_compare_to_;
};

The compilation fails in msvc2010 with:

error C2039: 'type' : is not a member of 'std::tr1::enable_if<_Test,_Type>'
1>          with
1>          [
1>              _Test=false,
1>              _Type=bool
1>          ]

in this case, iter_t is not contained in const_reverse_iterators_t and so
the 2nd operator() should not be enabled.

Rds,

MM