Fixes #691: Added a simple (and simplistic) optional_ref<T> class t…

…emplate

src/cuda/api/detail/optional_ref.hpp

@@ -0,0 +1,75 @@
+/**
+ * @file
+ *
+ * @brief An implementation of a simplistic optional-reference class
+ * (as optional<T&> is problematic semantically, and also probably not
+ * supported by this library's simplistic @ref optional implementation)
+ *
+ */
+#ifndef CUDA_API_WRAPPERS_OPTIONAL_REF_HPP_
+#define CUDA_API_WRAPPERS_OPTIONAL_REF_HPP_
+
+#include "optional.hpp"
+
+namespace cuda {
+
+namespace detail_ {
+
+template<typename T>
+struct optional_ref {
+	optional_ref &operator=(const optional_ref &other) = default;
+
+	optional_ref &operator=(optional_ref &&other) = default;
+
+	optional_ref &operator=(const T &value) = delete;
+
+	optional_ref &operator=(const T &&value) = delete;
+
+	optional_ref() noexcept: ptr_(nullptr)
+	{ }
+
+	optional_ref(T& v) noexcept : ptr_(&v) 
+	{ }
+
+	optional_ref(const optional_ref &other) = default;
+
+	optional_ref(nullopt_t) noexcept : ptr_(nullptr) { }
+
+	~optional_ref() noexcept = default;
+
+	T& value() const
+	{ return *ptr_; }
+
+	T& value_or(T& fallback_ref) const
+	{
+		return has_value() ? value() : fallback_ref;
+	}
+
+	T& operator*() noexcept { return *ptr_; }
+	const T& operator*() const noexcept { return *ptr_; }
+	T* operator->() noexcept { return ptr_; }
+	const T* operator->() const noexcept { return ptr_; }
+
+	bool has_value() const noexcept
+	{ return ptr_ != nullptr; }
+
+	operator bool() const noexcept
+	{ return has_value(); }
+
+	void reset() noexcept
+	{ ptr_ = nullptr; }
+
+protected:
+	T* ptr_;
+};
+
+} // namespace detail_
+
+template<typename T>
+using optional_ref = cuda::detail_::optional_ref<T>;
+
+} // namespace cuda
+
+//#endif // __cplusplus >= 201402L
+
+#endif //CUDA_API_WRAPPERS_OPTIONAL_REF_HPP_