Started rework of Error/Report/Panic interface.

Added Option<T>/std::optional<T> interop overloads.

Added Option<T> & Box<T> {static,dynamic}_cast() helper functions.

Fortune for libexopt's current commit: Middle blessing − 中吉

include/boxed.h

@@ -60,12 +60,52 @@ namespace exopt::types { namespace boxed {
 			} return *this;
 		}
 
+		[[gnu::nonnull(1)]]
+		constexpr static Box<T> from_raw_ptr(T* ptr) noexcept {
+			return Box<T>{ std::unique_ptr<T>{ ptr } };
+		}
+		constexpr static Box<T> from_raw_ptr(std::unique_ptr<T>&& uniq) 
+#if DEBUG
+			{ if(__builtin_expect(!uniq, false)) throw ptr::NullException{};
+#else
+
+			noexcept {
+			_EO_ASSUME(uniq.get() != nullptr);
+#endif
+			return Box<T>{ std::move(uniq) };
+		}
+		[[gnu::returns_nonnull]]
+		constexpr T* get() const noexcept { return m_ptr.get(); }
+		[[gnu::returns_nonnull]]
+		constexpr T* release() noexcept { return m_ptr.release(); }
+
+		constexpr std::unique_ptr<T>&& into_unique() &&noexcept { return std::move(m_ptr); }
+
 	//TODO: Accessors, `(explicit?) operator std::unique_ptr<T> const&[&]`?, etc.
 
 		constexpr ~Box() = default;
 	private:
+		constexpr explicit Box(std::unique_ptr<T>&& ptr)
+			: m_ptr(std::move(ptr)) {
+			_EO_ASSUME(m_ptr.get());
+		}
+
 		std::unique_ptr<T> m_ptr; // Unique<T> m_ptr;
 	};
+
+	template<typename T, typename U> requires(requires(T&& o) { static_cast<U&&>(o); })
+	constexpr Box<U> static_box_cast(Box<T>&& b) noexcept { return Box<U>::from_raw_ptr(static_cast<U*>(b.release())); }
+
+	template<typename T, typename U> requires(requires(T&& o) { static_cast<U&&>(o); })
+	constexpr Box<U> dynamic_box_cast(Box<T>&& b) {	
+		auto* rel = b.release();
+		try {
+			return Box<U>::from_raw_ptr(std::addressof(dynamic_cast<U&&>(std::move(*rel))));
+		} catch(...) {
+			delete rel;
+			throw;
+		}
+	} //TODO: Overload for `const&` that does the type check *before* the copy allocation.
 }
 using boxed::Box;
 }

include/either.hh

@@ -247,6 +247,11 @@ namespace exopt::types {
 	/// Manually lifetime managed Cow<T>
 	using either::Cow;
 
+	/// Wither an owned T, or a live, mutable reference to T.
+	template<typename T>
+	using MaybedOwnedRef = Cow<std::reference_wrapper<T>>; //XXX: Will we have to specialise Cow<> to make this work? \
+			TODO: I need to re-deisgn it to use a trait like `Borrow` and `ToOwned`, and implement the `owned_type` and `reference_type` to be specialised differently for different types without having to specialise the enture Cow<> struct.
+
 	/// RC-lifetime managed Cow<T>
 	template<typename T>
 	using RcCow = Cow<std::shared_ptr<T>>;

include/error.hh

@@ -7,6 +7,7 @@
 #include "exopt.h"
 
 #include "optional.h"
+#include "either.h"
 #include "util.hh"
 
 
@@ -31,9 +32,9 @@ namespace exopt {
 
 		constexpr virtual std::string_view message() const noexcept =0;
 
-		constexpr virtual MaybeOwnedRef<Error> inner() noexcept { return {}; } //TODO: Maybe just use `std::optional<std::reference_wrapper<Error>>`
-		constexpr virtual MaybeOwned<Report> into_report() noexcept { /* TODO */ } // XXX: ^^
-		constexpr virtual MaybeOwned<Report> into_report() && noexcept { /* TODO: auto{*this}.into_report() */ }
+		constexpr virtual types::Option<Error&> inner() noexcept { return { std::nullopt }; } 
+		constexpr virtual types::MaybeOwned<Report> into_report() noexcept { /* TODO */ } //TODO: Maybe just use `std::optional<std::reference_wrapper<Error>>`? Or Box<Report&>?
+		constexpr virtual types::MaybeOwned<Report> into_report() && noexcept { /* TODO: auto{*this}.into_report() */ }
 
 		constexpr virtual ~Error() = default;
 	protected:

include/optional.h

@@ -1,6 +1,6 @@
 #pragma once
 
-
+#include <optional>
 #include <utility>
 #include <concepts>
 
@@ -21,6 +21,18 @@ namespace exopt::types { namespace optional [[gnu::visibility("internal")]] {
 		constexpr static inline auto sentinel = nullptr;
 	};
 
+	template<typename T>
+	struct null_optimise<std::reference_wrapper<T> > { constexpr static inline bool value = true;
+		using held_type = T*;
+		using type = std::reference_wrapper<T>;
+		constexpr static decltype(auto) convert_to_held(std::add_rvalue_reference_t<type> t) noexcept { return std::addressof(t.get()); }
+		constexpr static decltype(auto) convert_from_held(std::add_rvalue_reference_t<held_type> t) noexcept { return std::ref<T>(*t); }
+
+		constexpr static inline auto sentinel = nullptr;
+	};
+
+
+
 	template<typename T>
 	struct null_optimise<ptr::Unique<T> > { constexpr static inline bool value = true;
 		using held_type = T __restrict__*;
@@ -233,6 +245,7 @@ namespace exopt::types { namespace optional [[gnu::visibility("internal")]] {
 		constexpr ~none_t() noexcept = default;
 
 		constexpr none_t(std::nullptr_t) noexcept : none_t() {}
+		constexpr none_t(std::nullopt_t) noexcept : none_t() {}
 
 		constexpr operator std::nullptr_t() const noexcept { return nullptr; }
 	};
@@ -268,6 +281,14 @@ namespace exopt::types { namespace optional [[gnu::visibility("internal")]] {
 
 		constexpr static inline bool is_null_optimised = has_null_opt<T>;
 
+		constexpr friend void swap(Option& a, Option& b) noexcept {
+			using std::swap;
+			swap(a.inner_, b.inner_); //XXX: Swap the values if possible?
+		}
+
+		constexpr Option(std::optional<T>&& opt) noexcept requires(!std::is_void_v<T>)
+			: inner_( bool(opt) ? std::move(*opt) : nullptr ) {}
+
 		constexpr explicit Option(std::nullptr_t) noexcept : inner_(nullptr) {}
 		constexpr Option(none_t) noexcept : Option(nullptr) {}
 		constexpr ~Option() noexcept(std::is_nothrow_destructible_v<T>) {}
@@ -541,6 +562,24 @@ namespace exopt::types { namespace optional [[gnu::visibility("internal")]] {
 		// ---
 	};
 
+	template<typename T, typename U> requires(requires(T&& p) { static_cast<U&&>(p); })
+	constexpr Option<U> static_opt_cast(Option<T>&& p) noexcept 
+	{
+		if(bool(p))	return Option<U> { static_cast<U&&>(std::move(*p)) };
+		return Option<U> { nullptr };
+	}
+
+	template<typename T, typename U> requires(requires(T&& p) { static_cast<U&&>(p); })
+	constexpr Option<U> dynamic_opt_cast(Option<T>&& p)
+	{
+		if(T* ptr = p.try_get_value())
+			if(U* pv = dynamic_cast<U*>(ptr))
+				return Option<U> { std::move(*pv) };
+		
+		return Option<U> { nullptr };
+	}
+	
+
 	static_assert(sizeof(Option<void*>) > sizeof(void*), "Option<T*>: Bad null_opt size");
 	static_assert(alignof(Option<void*>) == alignof(void*), "Option<T*>: Bad null_opt align");
 	static_assert(sizeof(Option<ptr::NonNull<int>>) == sizeof(int*), "Option<NonNull<T>>: Bad null_opt size");
@@ -557,4 +596,5 @@ namespace exopt::types { namespace optional [[gnu::visibility("internal")]] {
 
 }
 using optional::Option;
+
 }

include/util.hh

@@ -129,10 +129,10 @@ namespace exopt { namespace util [[gnu::visibility("internal")]] {
 		{ m_uninit = std::move(c.m_uninit); return *this; }
 
 		constexpr T& operator=(T&& value) noexcept {
-			m_init = std::move(value);
+			m_init = std::move(value); return *this;
 		}
 		constexpr T& operator=(T const& copy) noexcept {
-			m_init = maybe_uninit{copy};
+			m_init = maybe_uninit{copy}; return *this; //XXX: These assignment operators may not be a good idea, we can't guarantee which active destriminant it is.
 		}
 
 		constexpr T& assume_init() & noexcept = delete;
@@ -153,7 +153,15 @@ namespace exopt { namespace util [[gnu::visibility("internal")]] {
 		constexpr ~maybe_uninit() noexcept {}
 
 		constexpr void assume_init_drop() noexcept(std::is_nothrow_destructible_v<T>)
-		{ m_init.~T(); }
+		{ m_init.~T(); m_uninit = {}; }
+
+		[[nodiscard]]
+		constexpr T assume_init_take() noexcept(std::is_nothrow_move_constructible_v<T>)
+		{
+			auto v = std::move(m_init);
+			assume_init_drop();
+			return v;
+		}
 
 		constexpr maybe_uninit<T> init(T&& value) noexcept(std::is_nothrow_move_constructible_v<T>)
 		{ return maybe_uninit<T>{std::move(value), EXPLICIT_INIT_TAG<EXPLICIT_INIT_MOVE>{}}; }