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-rw-r--r--src/mbgl/util/optional.hpp69
1 files changed, 69 insertions, 0 deletions
diff --git a/src/mbgl/util/optional.hpp b/src/mbgl/util/optional.hpp
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+++ b/src/mbgl/util/optional.hpp
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+#ifndef MAPBOX_UTIL_OPTIONAL_HPP
+#define MAPBOX_UTIL_OPTIONAL_HPP
+
+#include <type_traits>
+
+#include <mbgl/util/variant.hpp>
+
+namespace mapbox
+{
+namespace util
+{
+
+template <typename T> class optional
+{
+ static_assert(!std::is_reference<T>::value, "optional doesn't support references");
+
+ struct none_type
+ {
+ };
+
+ variant<none_type, T> variant_;
+
+ public:
+ optional() = default;
+
+ optional(optional const &rhs)
+ {
+ if (this != &rhs)
+ { // protect against invalid self-assignment
+ variant_ = rhs.variant_;
+ }
+ }
+
+ optional(T const &v) { variant_ = v; }
+
+ explicit operator bool() const noexcept { return variant_.template is<T>(); }
+
+ T const &get() const { return variant_.template get<T>(); }
+ T &get() { return variant_.template get<T>(); }
+
+ T const &operator*() const { return this->get(); }
+ T operator*() { return this->get(); }
+
+ optional &operator=(T const &v)
+ {
+ variant_ = v;
+ return *this;
+ }
+
+ optional &operator=(optional const &rhs)
+ {
+ if (this != &rhs)
+ {
+ variant_ = rhs.variant_;
+ }
+ return *this;
+ }
+
+ template <typename... Args> void emplace(Args &&... args)
+ {
+ variant_ = T{std::forward<Args>(args)...};
+ }
+
+ void reset() { variant_ = none_type{}; }
+};
+}
+}
+
+#endif