custom variant type (replaces boost::variant and removes boost dependency altogether)

1 files changed, 380 insertions, 0 deletions

diff --git a/include/llmr/util/variant.hpp b/include/llmr/util/variant.hpp
new file mode 100644
index 0000000000..410aa8ead9
--- /dev/null
+++ b/include/llmr/util/variant.hpp
@@ -0,0 +1,380 @@
+#ifndef UTIL_VARIANT_HPP
+#define UTIL_VARIANT_HPP
+
+#include <utility>
+#include <typeinfo>
+#include <type_traits>
+#include <algorithm> // std::move/swap
+#include <stdexcept> // runtime_error
+#include <new> // operator new
+#include <cstddef> // size_t
+#include <iosfwd>
+
+#ifdef NDEBUG
+ #define VARIANT_INLINE inline __attribute__((always_inline))
+#else
+ #define VARIANT_INLINE __attribute__((noinline))
+#endif
+
+namespace util {
+
+namespace detail {
+
+static constexpr std::size_t invalid_value = std::size_t(-1);
+
+template <typename T, typename...Types>
+struct type_traits;
+
+template <typename T, typename First, typename...Types>
+struct type_traits<T, First, Types...>
+{
+    static constexpr std::size_t id = std::is_same<T, First>::value ? sizeof...(Types) : type_traits<T, Types...>::id;
+};
+
+template <typename T>
+struct type_traits<T>
+{
+    static constexpr std::size_t id = invalid_value;
+};
+
+template <typename T, typename...Types>
+struct is_valid_type;
+
+template <typename T, typename First, typename... Types>
+struct is_valid_type<T,First,Types...>
+{
+    static constexpr bool value = std::is_same<T,First>::value
+        || is_valid_type<T,Types...>::value;
+};
+
+template <typename T>
+struct is_valid_type<T> : std::false_type {};
+
+}
+
+template <std::size_t arg1, std::size_t ... others>
+struct static_max;
+
+template <std::size_t arg>
+struct static_max<arg>
+{
+    static const std::size_t value = arg;
+};
+
+template <std::size_t arg1, std::size_t arg2, std::size_t ... others>
+struct static_max<arg1, arg2, others...>
+{
+    static const std::size_t value = arg1 >= arg2 ? static_max<arg1, others...>::value :
+        static_max<arg2, others...>::value;
+};
+
+template<typename... Types>
+struct variant_helper;
+
+template<typename T, typename... Types>
+struct variant_helper<T, Types...>
+{
+    VARIANT_INLINE static void destroy(std::size_t id, void * data)
+    {
+        if (id == sizeof...(Types))
+        {
+            reinterpret_cast<T*>(data)->~T();
+        }
+        else
+        {
+            variant_helper<Types...>::destroy(id, data);
+        }
+    }
+
+    VARIANT_INLINE static void move(const std::size_t old_t, void * old_v, void * new_v)
+    {
+        if (old_t == sizeof...(Types))
+        {
+            new (new_v) T(std::move(*reinterpret_cast<T*>(old_v)));
+            //std::memcpy(new_v, old_v, sizeof(T));
+            // ^^  DANGER: this should only be considered for relocatable types e.g built-in types
+            // Also, I don't see any measurable performance benefit just yet
+        }
+        else
+        {
+            variant_helper<Types...>::move(old_t, old_v, new_v);
+        }
+    }
+
+    VARIANT_INLINE static void copy(const std::size_t old_t, const void * old_v, void * new_v)
+    {
+        if (old_t == sizeof...(Types))
+        {
+            new (new_v) T(*reinterpret_cast<const T*>(old_v));
+        }
+        else
+        {
+            variant_helper<Types...>::copy(old_t, old_v, new_v);
+        }
+    }
+};
+
+template<> struct variant_helper<>
+{
+    VARIANT_INLINE static void destroy(const std::size_t, void *) {}
+    VARIANT_INLINE static void move(const std::size_t, void *, void *) {}
+    VARIANT_INLINE static void copy(const std::size_t, const void *, void *) {}
+};
+
+namespace detail {
+
+template <typename F, typename V, typename...Types>
+struct dispatcher;
+
+template <typename F, typename V, typename T, typename...Types>
+struct dispatcher<F,V,T,Types...>
+{
+    typedef typename std::result_of<F(V const&)>::type result_type;
+    VARIANT_INLINE static result_type apply(V const& v, F f)
+    {
+        if (v.get_type_id() == sizeof...(Types))
+        {
+            return f(v. template get<T>());
+        }
+        else
+        {
+            return dispatcher<F,V,Types...>::apply(v, f);
+        }
+    }
+};
+
+template<typename F,typename V>
+struct dispatcher<F,V>
+{
+    typedef typename std::result_of<F(V const&)>::type result_type;
+    VARIANT_INLINE static result_type apply(V const&, F)
+    {
+        throw std::runtime_error("dispatch: FAIL");
+    }
+};
+
+// comparator functors
+struct equal_comp
+{
+    template <typename T>
+    bool operator()(T const& lhs, T const& rhs) const
+    {
+        return lhs == rhs;
+    }
+};
+
+struct less_comp
+{
+    template <typename T>
+    bool operator()(const T& lhs, const T& rhs) const
+    {
+        return lhs < rhs;
+    }
+};
+
+template <typename Variant, typename Comp>
+struct comparer
+{
+public:
+    explicit comparer(Variant const& lhs) noexcept
+        : lhs_(lhs) {}
+    comparer& operator=(const comparer&) = delete;
+    // visitor
+    template<typename T>
+    bool operator()(T const& rhs_content) const
+    {
+        T const& lhs_content = lhs_.template get<T>();
+        return Comp()(lhs_content, rhs_content);
+    }
+private:
+    Variant const& lhs_;
+};
+
+// operator<< helper
+template <typename Out>
+struct printer
+{
+public:
+    explicit printer(Out & out)
+        : out_(out) {}
+    printer& operator=(const printer&) = delete;
+
+// visitor
+    template <typename T>
+    void operator()(const T& operand) const
+    {
+        out_ << operand;
+    }
+private:
+    Out & out_;
+};
+
+} // detail
+
+template<typename... Types>
+struct variant
+{
+private:
+
+    static const std::size_t data_size = static_max<sizeof(Types)...>::value;
+    static const std::size_t data_align = static_max<alignof(Types)...>::value;
+
+    using data_t = typename std::aligned_storage<data_size, data_align>::type;
+
+    using helper_t = variant_helper<Types...>;
+
+    std::size_t type_id;
+    data_t data;
+
+public:
+
+    VARIANT_INLINE variant()
+        : type_id(detail::invalid_value) {}
+
+    template <typename T>
+    VARIANT_INLINE explicit variant(T const& val) noexcept
+        : type_id(detail::type_traits<T, Types...>::id)
+    {
+        static_assert(detail::is_valid_type<T,Types...>::value, "Not a valid type for this variant");
+        new (&data) T(val);
+    }
+
+    template <typename T>
+    VARIANT_INLINE variant(T && val) noexcept
+        : type_id(detail::type_traits<T,Types...>::id)
+    {
+        static_assert(detail::is_valid_type<T,Types...>::value, "Not a valid type for this variant");
+        new (&data) T(std::forward<T>(val)); // nothrow
+    }
+
+    VARIANT_INLINE variant(variant<Types...> const& old)
+        : type_id(old.type_id)
+    {
+        helper_t::copy(old.type_id, &old.data, &data);
+    }
+
+    VARIANT_INLINE variant(variant<Types...>&& old) noexcept
+        : type_id(old.type_id)
+    {
+        helper_t::move(old.type_id, &old.data, &data);
+    }
+
+    friend void swap(variant<Types...> & first, variant<Types...> & second)
+    {
+        using std::swap; //enable ADL
+        swap(first.type_id, second.type_id);
+        swap(first.data, second.data);
+    }
+
+    VARIANT_INLINE variant<Types...>& operator= (variant<Types...> other)
+    {
+        swap(*this, other);
+        return *this;
+    }
+
+    template<typename T>
+    VARIANT_INLINE void is() const
+    {
+        return (type_id == detail::type_traits<T, Types...>::id);
+    }
+
+    VARIANT_INLINE void valid() const
+    {
+        return (type_id != detail::invalid_value);
+    }
+
+    template<typename T, typename... Args>
+    VARIANT_INLINE void set(Args&&... args)
+    {
+        helper_t::destroy(type_id, &data);
+        new (&data) T(std::forward<Args>(args)...);
+        type_id = detail::type_traits<T,Types...>::id;
+    }
+
+    template<typename T>
+    VARIANT_INLINE T& get()
+    {
+        if (type_id == detail::type_traits<T,Types...>::id)
+        {
+            return *reinterpret_cast<T*>(&data);
+        }
+        else
+        {
+            throw std::runtime_error("in get()");
+        }
+    }
+
+    template<typename T>
+    VARIANT_INLINE T const& get() const
+    {
+        if (type_id == detail::type_traits<T,Types...>::id)
+        {
+            return *reinterpret_cast<T const*>(&data);
+        }
+        else
+        {
+            throw std::runtime_error("in get()");
+        }
+    }
+
+    VARIANT_INLINE std::size_t get_type_id() const
+    {
+        return type_id;
+    }
+
+    // visitor
+    template <typename F, typename V>
+    typename std::result_of<F(V const&)>::type
+    VARIANT_INLINE static visit(V const& v, F f)
+    {
+        return detail::dispatcher<F, V, Types...>::apply(v, f);
+    }
+
+    ~variant() noexcept
+    {
+        helper_t::destroy(type_id, &data);
+    }
+
+    // comparison operators
+    // equality
+    VARIANT_INLINE bool operator==(variant const& rhs) const
+    {
+        if (this->get_type_id() != rhs.get_type_id())
+            return false;
+        detail::comparer<variant, detail::equal_comp> visitor(*this);
+        return visit(rhs, visitor);
+    }
+    // less than
+    VARIANT_INLINE bool operator<(variant const& rhs) const
+    {
+        if (this->get_type_id() != rhs.get_type_id())
+        {
+            return this->get_type_id() < rhs.get_type_id();
+            // ^^ borrowed from boost::variant
+        }
+        detail::comparer<variant, detail::less_comp> visitor(*this);
+        return visit(rhs, visitor);
+    }
+};
+
+// unary visitor interface
+template <typename V, typename F>
+typename std::result_of<F(V const&)>::type
+VARIANT_INLINE static apply_visitor(V const& v, F f)
+{
+    return V::visit(v,f);
+}
+
+// operator<<
+template <typename charT, typename traits, typename Variant>
+VARIANT_INLINE std::basic_ostream<charT,traits>&
+operator<< (std::basic_ostream<charT,traits>& out, Variant const& rhs)
+{
+    detail::printer<std::basic_ostream<charT,traits> > visitor(out);
+    apply_visitor(rhs, visitor);
+    return out;
+}
+
+}
+
+#endif  // UTIL_VARIANT_HPP