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// file      : butl/optional -*- C++ -*-
// copyright : Copyright (c) 2014-2016 Code Synthesis Ltd
// license   : MIT; see accompanying LICENSE file

#ifndef BUTL_OPTIONAL
#define BUTL_OPTIONAL

#include <utility> // move()

namespace butl
{
  // Simple optional class template while waiting for std::optional.
  //
  struct nullopt_t {constexpr explicit nullopt_t (int) {}};
  constexpr const nullopt_t nullopt (1);

  template <typename T>
  class optional
  {
  public:
    typedef T value_type;

    optional (): null_ (true) {}
    optional (nullopt_t): null_ (true) {}
    optional (const T& v): value_ (v), null_ (false) {}
    optional (T&& v): value_ (std::move (v)), null_ (false) {}

    optional& operator= (nullopt_t) {value_ = T (); null_ = true; return *this;}
    optional& operator= (const T& v) {value_ = v; null_ = false; return *this;}
    optional& operator= (T&& v) {value_ = std::move (v); null_ = false; return *this;}

    T&       value () {return value_;}
    const T& value () const {return value_;}

    T*       operator-> () {return &value_;}
    const T* operator-> () const {return &value_;}

    T&       operator* () {return value_;}
    const T& operator* () const {return value_;}

    explicit operator bool () const {return !null_;}

  private:
    T value_;
    bool null_;
  };

  template <typename T>
  inline auto
  operator== (const optional<T>& x, const optional<T>& y) -> decltype (*x == *y)
  {
    return static_cast<bool> (x) == static_cast<bool> (y) && (!x || *x == *y);
  }

  template <typename T>
  inline auto
  operator!= (const optional<T>& x, const optional<T>& y) -> decltype (x == y)
  {
    return !(x == y);
  }
}

#endif // BUTL_OPTIONAL