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+// file : butl/optional -*- C++ -*-
+// copyright : Copyright (c) 2014-2015 Code Synthesis Ltd
+// license : MIT; see accompanying LICENSE file
+
+#ifndef BUTL_OPTIONAL
+#define BUTL_OPTIONAL
+
+namespace butl
+{
+ // Simple optional class template while waiting for std::optional.
+ //
+ template <typename T>
+ class optional
+ {
+ public:
+ typedef T value_type;
+
+ optional (): null_ (true) {}
+ optional (const T& v): value_ (v), null_ (false) {}
+ optional& operator= (const T& v) {value_ = 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_;
+ };
+}
+
+#endif // BUTL_OPTIONAL