1 files changed, 96 insertions, 0 deletions
diff --git a/libbutl/optional.hxx b/libbutl/optional.hxx
new file mode 100644
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--- /dev/null
+++ b/libbutl/optional.hxx
@@ -0,0 +1,96 @@
+// file      : libbutl/optional.hxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2017 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUTL_OPTIONAL_HXX
+#define LIBBUTL_OPTIONAL_HXX
+
+#include <utility>    // move()
+#include <functional> // hash
+
+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;
+
+    constexpr optional (): value_ (), null_ (true) {} // VC14 needs value_().
+    constexpr optional (nullopt_t): value_ (), null_ (true) {}
+    constexpr optional (const T& v): value_ (v), null_ (false) {}
+    constexpr 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_;}
+
+    bool         has_value () const {return !null_;}
+    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);
+  }
+
+  template <typename T>
+  inline auto
+  operator< (const optional<T>& x, const optional<T>& y) -> decltype (*x < *y)
+  {
+    bool px (x), py (y);
+    return px < py || (px && py && *x < *y);
+  }
+
+  template <typename T>
+  inline auto
+  operator> (const optional<T>& x, const optional<T>& y) -> decltype (*x > *y)
+  {
+    return y < x;
+  }
+}
+
+namespace std
+{
+  template <typename T>
+  struct hash<butl::optional<T>>: hash<T>
+  {
+    using argument_type = butl::optional<T>;
+
+    size_t
+    operator() (const butl::optional<T>& o) const
+      noexcept (noexcept (hash<T> {} (*o)))
+    {
+      return o ? hash<T>::operator() (*o) : static_cast<size_t> (-3333);
+    }
+  };
+}
+
+#endif // LIBBUTL_OPTIONAL_HXX