implement screens

1 files changed, 55 insertions, 0 deletions

diff --git a/lib/nes/common/box.hh b/lib/nes/common/box.hh
new file mode 100644
index 0000000..442d60f
--- /dev/null
+++ b/lib/nes/common/box.hh
@@ -0,0 +1,55 @@
+#pragma once
+
+namespace nes
+{
+	/// Wrapper around an object, allowing for it to be uninitialized or reassigned even if the object type doesn't
+	/// support it.
+	///
+	/// Basically a std::unique_ptr but stored in-place (and thus not movable).
+	template<typename T>
+	class box
+	{
+		bool initialized_{ false };
+		alignas(T) unsigned char buffer_[sizeof(T)];
+
+	public:
+		/// Create an empty box.
+		explicit box() = default;
+
+		~box()
+		{
+			clear();
+		}
+
+		box(box const&) = delete;
+		box(box&&) = delete;
+		auto operator=(box const&) -> box& = delete;
+		auto operator=(box&&) -> box& = delete;
+
+		auto operator*() -> T& { return *get(); }
+		auto operator*() const -> T const& { return *get(); }
+		auto operator->() -> T* { return get(); }
+		auto operator->() const -> T const* { return get(); }
+		operator bool() const { return has_value(); }
+
+		auto has_value() const -> bool { return initialized_; }
+		auto get() -> T* { return has_value() ? std::launder(reinterpret_cast<T*>(buffer_)) : nullptr; }
+		auto get() const -> T const* { return has_value() ? std::launder(reinterpret_cast<T const *>(buffer_)) : nullptr; }
+
+		/// Construct a new value in-place, potentially replacing the old value.
+		template<typename... Args>
+		auto emplace(Args&&... args) -> void
+		{
+			clear();
+			new (buffer_) T(std::forward<Args>(args)...);
+			initialized_ = true;
+		}
+
+		/// Clear the boxed value.
+		auto clear() -> void
+		{
+			if (initialized_) { (*this)->~T(); }
+			initialized_ = false;
+		}
+	};
+} // namespace nes
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