1 files changed, 149 insertions, 0 deletions
diff --git a/common/aloptional.h b/common/aloptional.h
new file mode 100644
index 00000000..269cba0e
--- /dev/null
+++ b/common/aloptional.h
@@ -0,0 +1,149 @@
+#ifndef AL_OPTIONAL_H
+#define AL_OPTIONAL_H
+
+#include <initializer_list>
+#include <type_traits>
+#include <utility>
+
+#include "almalloc.h"
+
+namespace al {
+
+#define REQUIRES(...) bool rt_=true, typename std::enable_if<rt_ && (__VA_ARGS__),bool>::type = true
+
+struct nullopt_t { };
+struct in_place_t { };
+
+constexpr nullopt_t nullopt{};
+constexpr in_place_t in_place{};
+
+template<typename T>
+class optional {
+    bool mHasValue{false};
+    union {
+        char mDummy[sizeof(T)]{};
+        T mValue;
+    };
+
+    template<typename... Args>
+    void DoConstruct(Args&& ...args)
+    {
+        ::new (std::addressof(mValue)) T{std::forward<Args>(args)...};
+        mHasValue = true;
+    }
+
+public:
+    using value_type = T;
+
+    optional() noexcept = default;
+    optional(nullopt_t) noexcept { }
+    template<REQUIRES(std::is_copy_constructible<T>::value)>
+    optional(const optional &rhs) { if(rhs) DoConstruct(*rhs); }
+    template<REQUIRES(std::is_move_constructible<T>::value)>
+    optional(optional&& rhs) { if(rhs) DoConstruct(std::move(*rhs)); }
+    template<typename... Args, REQUIRES(std::is_constructible<T, Args...>::value)>
+    explicit optional(in_place_t, Args&& ...args) : mHasValue{true}
+      , mValue{std::forward<Args>(args)...}
+    { }
+    template<typename U, typename... Args, REQUIRES(std::is_constructible<T, std::initializer_list<U>&, Args...>::value)>
+    explicit optional(in_place_t, std::initializer_list<U> il, Args&& ...args)
+      : mHasValue{true}, mValue{il, std::forward<Args>(args)...}
+    { }
+    template<typename U=value_type, REQUIRES(std::is_constructible<T, U&&>::value &&
+        !std::is_same<typename std::decay<U>::type, in_place_t>::value &&
+        !std::is_same<typename std::decay<U>::type, optional<T>>::value &&
+        std::is_constructible<U&&, T>::value)>
+    constexpr explicit optional(U&& value) : mHasValue{true}, mValue{std::forward<U>(value)}
+    { }
+    template<typename U=value_type, REQUIRES(std::is_constructible<T, U&&>::value &&
+        !std::is_same<typename std::decay<U>::type, in_place_t>::value &&
+        !std::is_same<typename std::decay<U>::type, optional<T>>::value &&
+        !std::is_constructible<U&&, T>::value)>
+    constexpr optional(U&& value) : mHasValue{true}, mValue{std::forward<U>(value)}
+    { }
+    ~optional() { if(mHasValue) al::destroy_at(std::addressof(mValue)); }
+
+    optional& operator=(nullopt_t) noexcept { reset(); return *this; }
+    template<REQUIRES(std::is_copy_constructible<T>::value && std::is_copy_assignable<T>::value)>
+    optional& operator=(const optional &rhs)
+    {
+        if(!rhs)
+            reset();
+        else if(*this)
+            mValue = *rhs;
+        else
+            DoConstruct(*rhs);
+        return *this;
+    }
+    template<REQUIRES(std::is_move_constructible<T>::value && std::is_move_assignable<T>::value)>
+    optional& operator=(optional&& rhs)
+    {
+        if(!rhs)
+            reset();
+        else if(*this)
+            mValue = std::move(*rhs);
+        else
+            DoConstruct(std::move(*rhs));
+        return *this;
+    }
+    template<typename U=T, REQUIRES(std::is_constructible<T, U>::value &&
+        std::is_assignable<T&, U>::value &&
+        !std::is_same<typename std::decay<U>::type, optional<T>>::value &&
+        (!std::is_same<typename std::decay<U>::type, T>::value ||
+        !std::is_scalar<U>::value))>
+    optional& operator=(U&& rhs)
+    {
+        if(*this)
+            mValue = std::forward<U>(rhs);
+        else
+            DoConstruct(std::forward<U>(rhs));
+        return *this;
+    }
+
+    const T* operator->() const { return std::addressof(mValue); }
+    T* operator->() { return std::addressof(mValue); }
+    const T& operator*() const& { return mValue; }
+    T& operator*() & { return mValue; }
+    const T&& operator*() const&& { return std::move(mValue); }
+    T&& operator*() && { return std::move(mValue); }
+
+    operator bool() const noexcept { return mHasValue; }
+    bool has_value() const noexcept { return mHasValue; }
+
+    T& value() & { return mValue; }
+    const T& value() const& { return mValue; }
+    T&& value() && { return std::move(mValue); }
+    const T&& value() const&& { return std::move(mValue); }
+
+    template<typename U>
+    T value_or(U&& defval) const&
+    { return bool{*this} ? **this : static_cast<T>(std::forward<U>(defval)); }
+    template<typename U>
+    T value_or(U&& defval) &&
+    { return bool{*this} ? std::move(**this) : static_cast<T>(std::forward<U>(defval)); }
+
+    void reset() noexcept
+    {
+        if(mHasValue)
+            al::destroy_at(std::addressof(mValue));
+        mHasValue = false;
+    }
+};
+
+template<typename T>
+inline optional<typename std::decay<T>::type> make_optional(T&& arg)
+{ return optional<typename std::decay<T>::type>{in_place, std::forward<T>(arg)}; }
+
+template<typename T, typename... Args>
+inline optional<T> make_optional(Args&& ...args)
+{ return optional<T>{in_place, std::forward<Args>(args)...}; }
+
+template<typename T, typename U, typename... Args>
+inline optional<T> make_optional(std::initializer_list<U> il, Args&& ...args)
+{ return optional<T>{in_place, il, std::forward<Args>(args)...}; }
+
+#undef REQUIRES
+
+} // namespace al
+
+#endif /* AL_SPAN_H */