Changed `NullException` to add optional type information. Added constexpr util::type_of<T>(), added constexpr `std::string_view` concatenation: `util::concat_str_v<std::string_view...>`, added `std::string_view util::concat_strings(auto const&...)`.

Fortune for libexopt's current commit: Future blessing − 末吉

include/array.h

@@ -0,0 +1,123 @@
+#pragma once
+
+#include <array>
+#include <utility>
+#include <memory>
+
+#include "pointer.h"
+#include "util.hh"
+
+#include "exopt.h"
+
+namespace exopt::types {
+	namespace polyarray [[gnu::visibility("internal")]] {
+
+		template<typename T, size_t N>
+		struct SizedArray;
+
+		struct UnsizedAccessor {
+			constexpr virtual ~UnsizedAccessor() = default;
+
+			constexpr virtual T* data() const noexcept =0;
+		};
+
+		template<typename T, size_t N>
+		struct SizedAccessor : virtual UnsizedAccessor {
+			//using UnsizedAccessor::UnsizedAccessor;
+			constexpr virtual ~SizedAccessor() = default;
+
+			constexpr T* data() const noexcept override final { return raw()->data(); }
+
+			[[gnu::returns_nonnull]]
+			constexpr virtual std::array<T, N>* raw() noexcept =0;
+			[[gnu::returns_nonnull]]
+			constexpr virtual std::array<T, N> const* raw() const noexcept =0;
+
+			constexpr virtual std::array<T, N>& array() & noexcept { return *raw(); }
+			constexpr virtual std::array<T, N> const& array() const& noexcept { return *raw(); }
+
+			constexpr virtual std::array<T, N>&& array() && noexcept { return std::move(*raw()); }
+			constexpr virtual std::array<T, N> const&& array() const&& noexcept { return std::move(*raw()); }
+		};
+
+		/// An `std::array<T>` with unknown compile-time size.
+		template<typename T>
+		class PolyArray : public virtual UnsizedAccessor {
+		public:
+			constexpr PolyArray() noexcept = default;
+			constexpr virtual ~PolyArray() = default;
+
+			using UnsizedAccessor::data; //constexpr virtual T* data() const noexcept =0; Inherited from UnsizedAccessor
+			constexpr virtual size_t size() const noexcept =0;
+			//TODO: std::array-like accessors based on `data()..size()`
+
+			template<size_t N>
+			constexpr std::array<T, N>* try_downcast() noexcept {
+				if consteval {
+					static_assert(size() == N, "Invalid downcast array size");
+				}
+				if (size() == N) { return static_cast<SizedAccessor<T, N>*>(accessor())->raw(); }   //reinterpret_cast<std::array<T, N>*>(unsafe_data()); } 
+				return nullptr;
+			}
+			template<size_t N>
+			constexpr std::array<T, N>&& downcast() && {
+				if(auto* nar = try_downcast()) {
+					return std::move(*nar);
+				} else throw_invalid_size();
+			}
+
+			constexpr bool empty() const noexcept { return !size(); }
+		protected:
+			[[noreturn, gnu::noinline, gnu::cold]]
+			constexpr void throw_invalid_size() {
+				std::terminate(); //TODO: throw `poly_array_size_exception`
+			}
+
+		private:
+			[[gnu::returns_nonnull]]
+			constexpr UnsizedAccessor* accessor() noexcept { return static_cast<UnsizedAccessor*>(this); }
+			[[gnu::returns_nonnull]]
+			constexpr const UnsizedAccessor* accessor() const noexcept { return static_cast<UnsizedAccessor const*>(this); }
+
+			template<size_t N>
+			[[gnu::returns_nonnull]]
+			constexpr SizedAccessor<T, N>* unsafe_cast() noexcept { return static_cast<SizedAccessor<T, N>*>(
+											static_cast<UnsizedAccessor*>(this)); }
+
+		};
+
+		template<typename T, size_t N>
+		struct SizedArray :  virtual /*XXX: Needed? since both non-virtual bases of this class have virtual base UnsizedAccessor?*/ SizedAccessor<T, N>
+				  , public PolyArray<T> {
+			[[gnu::const]]
+			constexpr size_t size() const noexcept override final { return N; }
+			//[[gnu::const, gnu::returns_nonnull]] // Unneeded, SizedAccessor implements it as raw()->data()
+			//constexpr T* data() const noexcept override final { return m_data.data(); }
+
+			constexpr SizedArray(std::array<T, N>&& m) noexcept
+				: m_data(std::move(m)) {}
+			//TODO: ctors, assign, etc.
+
+			constexpr virtual ~SizedArray() = default;
+			//TODO: operator*() decltype(auto) forwards from SizedAccessor::array()
+		protected:
+			[[gnu::returns_nonnull]]
+			constexpr std::array<T, N>* raw() noexcept override final { return std::addressof(m_data); }
+			[[gnu::returns_nonnull]]
+			constexpr std::array<T, N> const* raw() const noexcept override final { return std::addressof(m_data); }
+		private:
+			std::array<T, N> m_data;
+		};
+
+		template<typename T, size_t N>
+		constexpr std::unique_ptr<PolyArray<T>> make_unsized(std::array<T, N>&& array) noexcept {
+			auto sub = std::make_unique<SizedArray<T, N>>(std::move(array));
+			return std::unique_ptr<PolyArray<T>> { static_cast<PolyArray<T>*>(sub.release()) };
+		}
+
+		template<typename T, size_t N>
+		constexpr std::array<T, N>&& /*XXX: <- Is returning an rvalue-ref here acceptible? When is `array` dropped here? Does the caller actuall drop it or the std::move() in here...? We aren't actually assigning the move to anything at all, we're just working through rvalue-refs, so it *should* be fine...??? Fuck this language honestly... */ make_sized(std::unique_ptr<PolyArray<T>>&& array) {
+			return (*std::move(array)).downcast<T, N>();
+		}
+	}
+}

include/boxed.h

@@ -31,7 +31,7 @@ namespace exopt::types { namespace boxed {
 		requires(std::is_copy_constructible_v<T>)
 	{ if(__builtin_expect(!bool(c), false)) 
 #ifdef DEBUG
-		throw ptr::NullException{}; 
+		throw ptr::null_exception<T>{}; 
 #else
 		__builtin_unreachable(); 
 #endif
@@ -63,6 +63,86 @@ namespace exopt::types { namespace boxed {
 		{ static_cast<std::decay_t<To> &&>(from) } -> std::convertible_to<To>;
 	};
 
+	struct ErasedTypeDeleter { 
+		constexpr virtual ~ErasedTypeDeleter() = default;
+		constexpr ErasedTypeDeleter() noexcept = default;
+
+		constexpr virtual void apply_delete() = 0;
+		//TODO: See below...
+	};
+
+	template<polymorphic_castable<void> T>
+	constexpr auto uniq_erase_type(std::unique_ptr<T>&& from) noexcept {
+		//TODO: Overload case for `unique_ptr<T, D>` for `deleter` to apply (and contain) `D()` on back_cast()ed pointer T* instead of assuming default `delete`.
+		struct deleter final /*: public ErasedTypeDeleter XXX <- Is this useful, for unerasing the type, maybe?*/ {
+			typedef T type;
+
+			
+			/*[[gnu::cold, noreturn, gnu::noinline]]
+			constexpr static void _throw() 
+			{
+				throw ptr::NullException{};
+			}
+		public:*/
+			constexpr void opreator()(void *p) noexcept(std::is_nothrow_destructible_v<T>) {
+			/*	T* ptr;
+				if constexpr(DOES_CHECK) {
+				 if(__builtin_expect(!(ptr = dynamic_cast<T*>(p)), false))
+					_throw();
+				} else ptr = static_cast<T*>(p); 
+				delete ptr;*/
+				delete static_cast<T*>(p);
+			}
+			constexpr T* back_cast(void *p) noexcept { return static_cast<T*>(p); }
+			/*constexpr deleter() noexcept = default;
+			constexpr ~deleter() noexcept = default;*/
+		};
+		return std::unique_ptr<void, deleter> {
+			//XXX: Cannot retain type information of most-derived class from this: \
+			dynamic_cast<void*>	
+			static_cast<void*>
+			(std::move(from).release())
+			
+		};
+	}
+	template<polymorphic_castable<void> T, typename D> requires(requires{ typename std::unique_ptr<T, D>; })
+	constexpr auto uniq_erase_type(std::unique_ptr<T, D>&& from) noexcept {
+		class deleter final {
+			D m_del;
+		public:
+			constexpr void operator()(void* p) noexcept(std::is_nothrow_invocable_v<D::operator(), T>) {
+				m_del(static_cast<T*>(p));
+			}
+
+			constexpr T* back_cast(void* p) noexcept { return static_cast<T*>(p); }
+
+			constexpr deleter(D&& deleter) noexcept(std::is_nothrow_move_constructible_v<D>)
+				: m_del(std::move(deleter)) {}
+
+			constexpr deleter() noexcept(std::is_nothrow_default_constructible_v<D>) requires(std::is_default_constructible_v<D>) =default;//: m_del() {}
+
+			constexpr deleter(const deleter&) noexcept(std::is_nothrow_copy_constructible_v<D>) = default;
+			constexpr deleter(deleter&&) noexcept(std::is_nothrow_move_constructible_v<D>) = default;
+
+			constexpr deleter& operator=(const deleter&) noexcept(std::is_nothrow_copy_assignable_v<D>) = default;
+			constexpr deleter& operator=(deleter&&) noexcept(std::is_nothrow_move_assignable_v<D>) = default;
+
+			constexpr ~deleter() noexcept(std::is_nothrow_destructible_v<D>) {}
+		};
+		if constexpr(std::is_default_constructible_v<D>)
+			return std::unique_ptr<void, deleter> {
+				static_cast<void*>
+				(std::move(from).release()), deleter()
+			};
+		else {
+			deleter&& del{std::move(from.get_deleter())};
+			return std::unique_ptr<void, deleter> {
+				static_cast<void*>
+				(std::move(from).release()), deleter{std::move(del)}
+			};
+		}
+	}
+
 	template<typename To, typename From> requires(polymorphic_castable<From, To>)
 	constexpr std::unique_ptr<To> static_uniq_cast(std::unique_ptr<From>&& from) noexcept
 	{
@@ -102,6 +182,53 @@ namespace exopt::types { namespace boxed {
 	or (preferred): layout of Box<T> to be `{ aligned<T>(T, box_type_tag) } unique*` \
 		box_type_tag should be: One pointer width, starting at offset *T+1 (aligned to T within internal tuple struct), provides a way to access RTTI for `*T`, a pointer to static (non-allocated) type information or dynamic_cast used lambda would be ideal.
 #endif
+	/// Base class which is used to store the layout of Box<T>'s allocated memory. Intended for use to determine if a certain `T`'s `this` pointer is inside a `Box<T>` or not.
+	class dynamic_boxed_layout_base{
+		using Self = dynamic_boxed_layout_base;
+	public:
+		constexpr dynamic_boxed_layout_base() noexcept = default;
+		constexpr ~dynamic_boxed_layout_base() = default;
+
+		typedef void* (dynamic_cast_t)(Self*);
+		typedef const void* (dynamic_const_cast_t)(Self const*);
+
+		constexpr virtual size_t value_byte_offset() const noexcept =0;
+
+		[[gnu::returns_nonnull]]
+		constexpr void* extract_untyped_pointer() noexcept {
+			return reinterpret_cast<void*>(
+				reinterpret_cast<this>(unsigned char*) + value_byte_offset()
+			);
+		}
+		[[gnu::returns_nonnull]]
+		constexpr const void* extract_untyped_pointer() const noexcept {
+			return reinterpret_cast<void const*>(
+				reinterpret_cast<this>(const unsigned char*) + value_byte_offset()
+			);
+		}
+
+		constexpr virtual void* invoke_casting_shim(dynamic_cast_t const*) const noexcept =0;
+
+		template<typename T>
+		constexpr bool is_typeof() const noexcept { return invoke_casting_shim([] (Self* self) { return dynamic_cast<T*>(self)
+
+		template<typename T>
+		[[gnu::returns_nonnull]]
+		inline T* extract_pointer_unsafe() noexcept {
+			return reinterpret_cast<T*>(extract_untyped_pointer());
+		}
+		template<typename T>
+		[[gnu::returns_nonnull]]
+		inline const T* extract_pointer_unsafe() const noexcept {
+			return reinterpret_cast<const T*>(extract_untyped_pointer());
+		}
+
+		template<typename T>	
+		[[gnu::returns_nonnull]]
+		inline T* try_extract_pointer() noexcept {
+			return is_typeof<T>() ? extract_pointer_unsafe<T>() : nullptr;
+		}
+	};
 
 	template<typename T>
 	struct Box final {
@@ -179,18 +306,27 @@ namespace exopt::types { namespace boxed {
 			_EO_ASSUME(m_ptr.get());
 		}
 
-#if 0
 // TODO: Identifying if a value `this` pointer is boxed
-		struct alignas(type) inner_layout {
-			constexpr inner_layout() noexcept = default;
-			constexpr inner_layout(const inner_layout&) noexcept = default;
-			constexpr ~inner_layout() noexcept = default;
+		struct alignas(type) inner_layout_t final : public dynamic_boxed_layout_base {
+			using boxed_value_t = type;
+
+			constexpr inner_layout_t(type&& v) noexcept(std::is_nothrow_move_constructible_v<type>)
+				: value(std::move(v)) {}
+			//TODO: All the ctors, assigns, and operators that can make this newtype wrapper more conveniently useable as a deref-target for accessing `value`.
+			
+			constexpr /*virtual*/ ~inner_layout_t() = default;
+
+			[[gnu::const]]
+			constexpr size_t value_byte_offset() const noexcept override { return offsetof(inner_layout_t, value); }
 
 			type value;
-			box_type_tag identifier{box_tag_of<T>()};
 		};
-#endif
-		std::unique_ptr<T> m_ptr; // Unique<T> m_ptr;
+		
+		struct inner_unique_ptr_t final {
+			std::unique_ptr<inner_layout_t>
+		};
+
+		inner_unique_ptr_t m_ptr; // Unique<T> m_ptr;
 	};
 
 #define _EO_ADD_RV std::add_rvalue_reference_v

include/pointer.h

@@ -5,6 +5,11 @@
 #include <concepts>
 #include <bit>
 #include <stdexcept>
+#include <tuple>
+
+#include "util.hh"
+
+#define _EO_DETAILS namespace details [[gnu::visibility("internal")]]
 
 namespace exopt::ptr {	
 	template<typename T>
@@ -24,6 +29,13 @@ namespace exopt::ptr {
 	template<typename T>
 	using AliasedRef = T __attribute__((__may_alias__))&;
 
+	using opaque_t = void;
+	using address_t = uintptr_t;
+
+	constexpr inline size_t address_bits_v = sizeof(address_t) * 8;
+
+	static_assert(sizeof(RawPtr<opaque_t>) == sizeof(address_t), "Bad address_t width");
+
 	template<typename T, size_t Size>
 	concept IsSize = sizeof(T) == Size;
 
@@ -131,17 +143,53 @@ namespace exopt::ptr {
 		return *new T(std::forward<Args>(ctor)...);
 	}
 
-	struct NullException /*TODO : public error::Error*/ {
-		constexpr NullException() noexcept = default;
-		constexpr NullException(const NullException&) noexcept = default;
-		constexpr NullException& operator=(const NullException&) noexcept = default;
-		constexpr virtual ~NullException() noexcept {}
+	template<typename... Types>
+	struct NullDerefException : public NullDerefException<> {
+		using types = std::tuple<Types...>;	
+		using NullDerefException<>::NullDerefException;
+
+		constexpr std::string_view message() const noexcept override { 
+/*			constexpr auto value = util::concat_strings("pointer was null for types ", util::type_name<Types>()...);
+			return value;*/
+			return util::concat_str_v< std::string_view{"pointer was null for types "}, util::type_name<Types>()... >;
+		}
+		constexpr virtual ~NullDerefException() noexcept {}
+	};
+ 
+	template<>
+	struct NullDerefException<> /*TODO : public error::Error*/ {
+		constexpr NullDerefException() noexcept = default;
+		constexpr NullDerefException(const NullException&) noexcept = default;
+		constexpr NullDerefException& operator=(const NullException&) noexcept = default;
+		constexpr virtual ~NullDerefException() noexcept {}
 
-		constexpr std::string_view message() const noexcept /*override*/ { return "pointer was null"; }
+		constexpr virtual std::string_view message() const noexcept /*override*/ { return "pointer was null"; }
 
 		std::runtime_error as_runtime() &&noexcept; /*TODO: override*/ 
 	};
 
+	using NullException = NullDerefException<>;
+
+	template<typename T>
+	struct NullDerefException<T> : public NullDerefException<> {
+		using type = T;
+		using NullDerefException<>::NullDerefException;
+
+		constexpr std::string_view message() const noexcept override { 
+			return util::concat_str_v< std::string_view{"pointer was null for type "}, util::type_name<type>() >;
+		}
+		constexpr virtual ~NullDerefException() noexcept {}
+	};
+	
+	template<typename... Types>
+	consteval auto/*&&*/ null_exception() noexcept { 
+		/*NullException&& value = NullDerefException<Types...>{};
+		return std::move(value); <- this isn't actually what we want I'm pretty sure...*/
+		return NullDerefException<Types...>{};
+	}
+
+	consteval NullException/*&&*/ null_exception() noexcept { return {}; }
+
 	template<typename T> requires(!std::is_reference_v<T>)
 	struct NonNull {
 
@@ -330,4 +378,20 @@ namespace exopt::ptr {
 	}
 	static_assert(uniq_check(), "Invalid Unique<>.get()");
 #endif
+	_EO_DETAILS {
+		[[gnu::const]]
+		address_t hash(const opaque_t*) noexcept;
+	}
+
+
+	/// Hash a pointer and retrieve a scrambled, unique value representing that memory address.
+	[[gnu::const]]
+	constexpr address_t hash(const opaque_t* ptr) noexcept {
+		if consteval {
+			throw "TODO: How to hash pointer in constexpr context?";
+		} else {
+			return details::hash(ptr);
+		}
+	}
 }
+#undef _EO_DETAILS

include/rng.hh

@@ -0,0 +1,53 @@
+#pragma once
+
+#include <bit>
+#include <array>
+
+#include <cstdint>
+
+#include "util.hh"
+
+#include "exopt.h"
+
+namespace exopt::rng {
+	[[gnu::visibility("internal")]]
+	constexpr inline auto COMPILED_ENTROPY{
+#if __has_include("compiled_entropy.dat")
+#embed "compiled_entropy.dat"
+#else
+	nullptr 
+#endif
+	};
+	constexpr inline auto has_compiled_entropy_v = !std::is_same_v<std::nullptr_t, decltype(COMPILED_ENTROPY)>;
+
+	// XXX: The usage of __COUNTER__ *might* work as wanted if we wrap it in _EO_CONSTANT_VALUE() and take `util::comptime<uint64_t> auto = _EO_CONSTANT_VALUE(__COUNTER__)` as default argument instead. Maybe... I don't know..
+	template<typename T = unsigned char>
+	consteval decltype(auto) comptime_rand_next() noexcept {
+		std::array<unsigned char, sizeof(T)> v;
+		for(int i=0;i<v.size();i++) v[i] = comptime_rand_next<unsigned char>();
+		return util::comptime_value(std::bit_cast<T>(std::move(v)));
+	}
+	template<>
+	consteval decltype(auto) comptime_rand_next<unsigned char>(uint64_t counter = __COUNTER__) noexcept {
+		return _EO_CONSTANT_VALUE(COMPILED_ENTROPY[counter  % sizeof(COMPILED_ENTROPY)]);
+	}
+
+	consteval uint64_t seed_linear(uint64_t counter = __COUNTER__) noexcept { return uint64_t(counter); } //XXX: This is kinda a dumb experiment, the __TIME__ TU-specific seed should be fine, but __COUNTER__ is a token evaluated regardless of calling context, so... Unless it's used before the #include<>, it'll always be the same.
+	consteval uint64_t seed_translation() noexcept { return uint64_t(__TIME__); }
+
+	
+	// Seed: __TIME__ or __COUNTER__
+	[[gnu::const]]
+	constexpr uint64_t splitmix64_once(uint64_t x) noexcept {
+		//TODO: implement splitmix64 here for constexpr/consteval contexts
+	}
+	
+	constexpr inline uint64_t translation_unit_fixed_seed = splitmit64_once(seed_translation());
+	constexpr inline uint64_t linear_fixed_seed = splitmit64_once(seed_linear()); // ODR dependant?? When is __COUNTER__ evaluated? In preprocessing, right? So, before any compilation?
+	constexpr inline auto translation_unit_rolling_seed = ([] () {
+		struct {
+			constexpr operator uint64_t() const noexcept { return splitmix64_once(translation_unit_fixed_seed ^ seed_linear()) ^ _EO_CONSTANT_VALUE(splitmix64_once(__COUNTER__)); }
+		} inner;
+		return inner;
+	})();
+}

include/util.hh

@@ -89,6 +89,121 @@ namespace exopt { namespace util [[gnu::visibility("internal")]] {
 		return _array_create(std::move(a), _I{});
 	}
 
+	template<size_t N, typename A = std::array<char, N>, size_t... Idx>
+	constexpr A substring_literal_as(const auto& str, std::index_sequence<Idx...>) noexcept
+		requires(requires(size_t n) { 
+			{ str[n] } noexcept -> std::convertible_to<char>;
+		})
+	{
+		return { str[Idx]..., '\n' };
+	}
+	template<size_t... Idx>
+	constexpr auto substring_literal(const auto& str, std::index_sequence<Idx...>) noexcept
+		requires(std::is_invocable_v<substring_literal_as<sizeof...(Idx), std::array<char, sizeof...(Idx)>, Idx...>, decltype(str), std::index_sequence<Idx...>>)
+	{ return std::array{ str[Idx]..., '\n' }; }
+
+	template<typename T>
+	constexpr auto type_name_literal() noexcept 
+	{
+		constexpr std::string_view prefix	{
+#if defined(__clang__)
+			"[T = "
+#elif defined(__GNUC__)
+			"with T = "
+#else
+// Fuck MSVC, don't care.
+#error Unsupported compiler
+#endif
+		};
+		constexpr std::string_view suffix	{"]"};
+		constexpr std::string_view function	{__PRETTY_FUNCTION__};
+
+		constexpr auto start = function.find(prefix) + prefix.size();
+		constexpr auto end = function.rfind(suffix);
+
+		static_assert(start < end);
+
+		constexpr std::string_view name = function.substr(start, (end - start));
+		return substring_literal(name, std::make_index_sequence<name.size()>{});
+	}
+
+	template<typename T>
+	struct [[gnu::visibility("internal")]] type_name_of {
+		constexpr static inline auto value = type_name_literal<T>();
+
+		[[gnu::const]]
+		consteval operator std::string_view() const noexcept {
+			constexpr auto& v = value;
+			return std::string_view { v.data(), v.size() };
+		}
+	};
+
+	template<typename T>
+	constexpr auto type_name() noexcept -> std::string_view
+	{
+		constexpr auto& value = type_name_of<T>::value;
+		return std::string_view { value.data(), value.size() };
+	}
+
+	template<typename T>
+	constexpr inline auto type_name_v = type_name<T>();
+
+	template<typename S = std::string_view, S const&... Strs>
+	class [[gnu::visibility("internal")]] concat_str {
+		consteval static auto impl() noexcept
+		{
+			constexpr size_t len = (Strs.size() + ... + 0);
+			std::array<char, len+1> arr{};
+			auto append = [i=0, &arr](auto const& s) mutable {
+				for(auto c : s) arr[i++] = c;
+			};
+			(append(Strs), ...);
+			arr[len] = 0;
+			return arr;
+		}
+	public:
+		constexpr static inline auto literal = impl();
+		constexpr static inline S value { literal.data(), literal.size()-1 };
+	};
+
+	template<std::string_view const&... Ss>
+	constexpr static inline auto concat_str_v = concat_str<std::string_view, Ss...>::value;
+
+	template<typename S = std::string_view>
+	consteval S concat_strings(std::convertible_to<S> auto const&... strings) noexcept
+	{ 
+		return concat_str<S, S{strings}...>::value;
+	}
+
+	static_assert(concat_str_v< std::string_view{"hello"}, std::string_view{" "}, std::string_view{"view"} >
+			== std::string_view{"hello view"}, "concat_str_v<>: Concatenated string_view failed");
+
+	template<typename R, typename... Args>
+	constexpr auto map(auto const& fun, Args&&... values) noexcept((std::is_nothrow_invocable_v<decltype(fun), Args> && ...))
+								requires((std::is_invocable_v<decltype(fun), Args> && ...) and (
+			(std::is_void_v<std::invoke_result_t<decltype(fun), Args>> || ...) ||
+			 std::is_constructible_v<R, std::invoke_result_t<decltype(fun), Args>...>))
+		-> std::conditional_t< (std::is_void_v<std::invoke_result_t<decltype(fun), Args>> || ...)
+					, void
+					, R>
+	{
+		if constexpr( (std::is_void_v<std::invoke_result_t<decltype(fun), Args>> || ...) ) {
+			((void)std::invoke(fun, values),...);
+		} else return { std::invoke(fun, values)... };
+	}
+
+	//XXX: To allow this, we might have to turn `map` from a function into a function-object class... Eh. \
+		Or we can just let the user specify `R` by using std::tuple as the lvalue assigned from the call maybe? Or we might have to change it to a `template<template<typename... Results>, typename... Args>` function-object class; but that would break the `void` case.... Eeeehh, can we partial-specialise a template<template into a template<typename? I don't think we can on the surface without helper ''trait'' templates.... Eh......
+	template<typename... Args>
+	using map_tuple = map<std::tuple<Args...>, Args...>;
+
+	template<typename Fn, typename... Args> requires((std::is_invocable_v<Fn, Args> && ...))
+	constexpr void apply(const Fn& fun, Args&&... values) noexcept((std::is_nothrow_invocable_v<Fn, Args> && ...))
+		/*-> std::conditional_t<	(std::is_void_v<std::invoke_result_t<Fn, Args>> || ...)
+					, void
+					, std::common_type_t< std::invoke_result_t<Fn, Args>... > >*/
+	{ map<void, Args...>(fun, std::forward<Args>(values)...); }
+
 	struct [[gnu::visibility("internal")]]  CTInternalFatalError  {
 		constexpr CTInternalFatalError() noexcept = default;
 		constexpr CTInternalFatalError(CTInternalFatalError const&) noexcept = default;
@@ -102,29 +217,33 @@ namespace exopt { namespace util [[gnu::visibility("internal")]] {
 		consteval virtual std::string_view message() const noexcept =0;
 	};
 
+	/// Throw a string at runtime, as an `std::runtime_error`.
 	[[noreturn, gnu::noinline, gnu::cold]]
 	void throw_runtime(std::string_view&&);	
 
+	/// Throw a string at runtime, or halt compilation with a `CTInternalFatalError`
 	[[noreturn]]//, gnu::noinline, gnu::cold]]
 	constexpr void throw_runtime(std::convertible_to<std::string_view> auto&& msg) {
-		std::string_view view{msg};
 		if consteval {
-			using CTE = CTInternalFatalError; 
-			struct CTIFRuntimeError : public CTE {
+#define CTE CTInternalFatalError
+			using S = decltype(msg);
+			struct CTIFRuntimeError final : public CTE {
 				using CTE::CTE;
-				consteval CTIFRuntimeError(std::string_view&& view) noexcept
+				consteval CTIFRuntimeError(S&& view) noexcept
 					: CTE(), m_message(std::move(view)) {}
-				consteval std::string_view message() const noexcept override { return m_message; }
+				consteval std::string_view message() const noexcept override { return { m_message }; }
 				constexpr virtual ~CTIFRuntimeError() noexcept {}
 			private:
-				std::string_view m_message;
+				S m_message;
 			};
-			throw CTIFRuntimeError(std::move(view));
+#undef CTE
+			throw CTIFRuntimeError(std::move(msg));
 		} else {
-			throw_runtime(std::move(view));
+			static_cast<void (std::string_view&&)>(throw_runtime)({std::move(msg)}); //XXX: We may have to rename the above function (and make it [[internal]], or refactor to make it a private method of a function-object class `throw_runtime` to avoid ambiguations when constexpr-context calls it with the exact typed argument `std::string_view&&`... Maybe... I'm not really sure.
 		}
 		__builtin_unreachable();
 	}
+
 	// Returns an anonymous union with inavtive field: `T value` and active field `assume init` (no unique address).
 	template<typename T> requires(!std::is_reference_v<T>)
 	constexpr auto uninit() noexcept {

src/ptr.cpp

@@ -4,6 +4,17 @@
 
 #include "pointer.h"
 
+
 namespace exopt::ptr {
-	std::runtime_error NullException::as_runtime() &&noexcept { return std::runtime_error{std::string{message()} }; }
+	static_assert(address_bits_v == sizeof(address_t) * CHAR_BIT, "Bad CHAR_BIT: Must be 8");
+
+	std::runtime_error NullDerefException<>::as_runtime() &&noexcept { return std::runtime_error{std::string{message()} }; }
+
+	namespace details [[gnu::visibility("internal")]] {
+		[[gnu::const]]
+		address_t hash(const opaque_t* ptr) noexcept {
+			static_assert((address_bits_v & (64 | 32)) == address_bits_v, "Cannot hash pointer with address that is not 64 or 32 bits wide");
+			//TODO: Find good pointer hashing algorithm, or use crc64 (if constexpr(address_bits_v == 64), else crc32.)
+		}
+	}
 }