c++ - How to SFINAE out non-containers parameters -


i have template function want enable standard containers (or containers compatible standard containers, @ least provide begin() member function). i'm sfinae-ing out non-containers in following way:

template<typename container> typename container::value_type  f(const container& c,     typename std::enable_if<         std::is_same<             decltype(*c.begin()),             typename container::value_type         >::value     >::type* = nullptr) {     // implementation here }

the std::is_same , decltype don't elegant. there better way of doing this?

ps: need sfinae here because have different overload

template<typename derived> f(const eigen::matrixbase<derived>& a)

and whenever try f(some_eigen_matrix), container overload ends being picked up, compiler spits out error because type lacking begin().

using void_t, can make type trait having begin() , end() (and else might want check for, typename t::iterator, can keep piling expressions on):

template <typename t, typename = void> struct is_std_container : std::false_type { };  template <typename t> struct is_std_container<t,     void_t<decltype(std::declval<t&>().begin()),            decltype(std::declval<t&>().end()),            typename t::value_type            >>     : std::true_type { };

and sfinae on that:

template <typename container> typename std::enable_if<     is_std_container<container>::value,     typename container::value_type >::type  f(const container& c) { .. }

also, if wanted verify begin() gives t::iterator (or @ least they're equality comparable), can too:

void_t<     decltype(begin(std::declval<t&>()) == std::declval<typename t::iterator>()) >

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