From 10b6d51522e9590a12a748439193c4bc46e0f0b4 Mon Sep 17 00:00:00 2001
From: Bananymous <bananymousosq@gmail.com>
Date: Wed, 22 Feb 2023 01:17:21 +0200
Subject: [PATCH] BAN: implement Variant<> for two types

---
 BAN/include/BAN/Assert.h  |   8 +++
 BAN/include/BAN/Variant.h | 147 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 155 insertions(+)
 create mode 100644 BAN/include/BAN/Assert.h
 create mode 100644 BAN/include/BAN/Variant.h

diff --git a/BAN/include/BAN/Assert.h b/BAN/include/BAN/Assert.h
new file mode 100644
index 00000000..24114702
--- /dev/null
+++ b/BAN/include/BAN/Assert.h
@@ -0,0 +1,8 @@
+#pragma once
+
+#if defined(__is_kernel)
+	#include <kernel/Panic.h>
+	#define ASSERT(cond) do { if (!(cond)) Kernel::panic("ASSERT("#cond") failed"); } while(false)
+#else
+	#error "NOT IMPLEMENTED"
+#endif
\ No newline at end of file
diff --git a/BAN/include/BAN/Variant.h b/BAN/include/BAN/Variant.h
new file mode 100644
index 00000000..cf6d4d20
--- /dev/null
+++ b/BAN/include/BAN/Variant.h
@@ -0,0 +1,147 @@
+#pragma once
+
+#include <BAN/Assert.h>
+#include <BAN/Math.h>
+#include <BAN/Move.h>
+
+namespace BAN
+{
+
+	template<typename T1, typename T2>
+	class Variant
+	{
+	public:
+		static_assert(!is_same_v<T1, T2>);
+
+		Variant() = default;
+
+		Variant(const T1& value)	{ set(value); }
+		Variant(T1&& value)			{ set(move(value)); }
+		Variant(const T2& value)	{ set(value); }
+		Variant(T2&& value)			{ set(move(value)); }
+
+		Variant(const Variant<T1, T2>& other)	{ *this = other; }
+		Variant(Variant<T1, T2>&& other)		{ *this = move(other); }
+
+		~Variant() { clear(); }
+
+		Variant<T1, T2>& operator=(const Variant<T1, T2>& other);
+		Variant<T1, T2>& operator=(Variant<T1, T2>&& other);
+
+		template<typename U>
+		bool is() const;
+
+		template<typename U>
+		void set(U&&);
+		template<typename U>
+		void set(const U& value) { set(move(U(value))); } 
+
+		template<typename U>
+		const U& get() const;
+		template<typename U>
+		U& get();
+
+		void clear();
+
+	private:
+		static constexpr uint32_t m_size = Math::max(sizeof(T1), sizeof(T2));
+		uint8_t m_storage[m_size] = {};
+		uint32_t m_index = 0;
+	};
+
+	template<typename T1, typename T2>
+	Variant<T1, T2>& Variant<T1, T2>::operator=(const Variant<T1, T2>& other)
+	{
+		clear();
+		if (other.is<T1>())
+			set(other.get<T1>());
+		if (other.is<T2>())
+			set(other.get<T2>());
+		return *this;
+	}
+
+	template<typename T1, typename T2>
+	Variant<T1, T2>& Variant<T1, T2>::operator=(Variant<T1, T2>&& other)
+	{
+		clear();
+		if (other.is<T1>())
+			set(move(other.get<T1>()));
+		if (other.is<T2>())
+			set(move(other.get<T2>()));
+		other.clear();
+		return *this;
+	}
+
+	template<typename T1, typename T2>
+	template<typename U>
+	bool Variant<T1, T2>::is() const
+	{
+		if constexpr(is_same_v<T1, U>)
+			return m_index == 1;
+		if constexpr(is_same_v<T2, U>)
+			return m_index == 2;
+		return false;
+	}
+
+
+	template<typename T1, typename T2>
+	template<typename U>
+	void Variant<T1, T2>::set(U&& value)
+	{
+		static_assert(is_same_v<T1, U> || is_same_v<T2, U>);
+		clear();
+		if constexpr(is_same_v<T1, U>)
+		{
+			new (m_storage) T1(move(value));
+			m_index = 1;
+		}
+		if constexpr(is_same_v<T2, U>)
+		{
+			new (m_storage) T2(move(value));
+			m_index = 2;
+		}
+	}
+
+	template<typename T1, typename T2>
+	template<typename U>
+	const U& Variant<T1, T2>::get() const
+	{
+		static_assert(is_same_v<T1, U> || is_same_v<T2, U>);
+		if constexpr(is_same_v<T1, U>)
+		{
+			ASSERT(m_index == 1);
+			return *(T1*)m_storage;
+		}
+		if constexpr(is_same_v<T2, U>)
+		{
+			ASSERT(m_index == 2);
+			return *(T2*)m_storage;
+		}
+	}
+
+	template<typename T1, typename T2>
+	template<typename U>
+	U& Variant<T1, T2>::get()
+	{
+		static_assert(is_same_v<T1, U> || is_same_v<T2, U>);
+		if constexpr(is_same_v<T1, U>)
+		{
+			ASSERT(m_index == 1);
+			return *(T1*)m_storage;
+		}
+		if constexpr(is_same_v<T2, U>)
+		{
+			ASSERT(m_index == 2);
+			return *(T2*)m_storage;
+		}
+	}
+
+	template<typename T1, typename T2>
+	void Variant<T1, T2>::clear()
+	{
+		if (is<T1>()) ((T1*)m_storage)->~T1();
+		if (is<T2>()) ((T2*)m_storage)->~T2();
+		m_index = 0;
+	}
+
+}
\ No newline at end of file