cpp-lazy-stream/streams/traits.hpp

//
//  traits.hpp
//  stream
//
//  Created by Sam Jaffe on 6/24/17.
//

#pragma once

namespace stream { namespace detail {
  template <typename T>
  struct ref_or_val {
    ref_or_val operator=(T && val) { value = std::move(val); return *this; }
    operator T const &() const { return value; }
    T value;
  };
  
  template <typename T>
  struct ref_or_val<T&> {
    ref_or_val operator=(T & val) { value = &val; return *this; }
    operator T &() const { return *value; }
    T * value;
  };
} }

namespace stream { namespace detail {
  template <typename F> struct map_member_object;
  template <typename T, typename R>
  struct map_member_object<R T::*> {
    using type = R const &;
    type operator()(T const & val) const { return val.*mem; }
    R T::*mem;
  };
  
  template <typename F> struct map_member_function;
  template <typename T, typename R>
  struct map_member_function<R (T::*)() const> {
    using type = R;
    type operator()(T const & val) const { return (val.*mem)(); }
    R (T::* mem)() const;
  };
}}

namespace stream { namespace detail {
  template <typename T, typename = void>
  struct is_dereferencable : public std::false_type {};

  template <>
  struct is_dereferencable<void*> : public std::false_type {};
  
  template <typename T>
  struct is_dereferencable<T, typename std::enable_if<!std::is_void<decltype(*std::declval<T>())>::value>::type> : public std::true_type {};
}}