#pragma once
#include <utility>
#include <variant>

namespace meta
{
	// a struct stolen from rust
	// lets us define a result, or return an error otherwise
	template<typename Result, typename Error>
	class result
		: protected std::variant<Result, Error>
	{
	protected:
		using Base = std::variant<Result, Error>;
	private:
		static constexpr auto Success = 0;
		static constexpr auto Failure = 1;
		static_assert(std::is_default_constructible_v<Error>, "Error must be default constructible");
	public:
		using value_type = Result;
		using Base::Base;
		using Base::operator=;

		// accessors
		Result& value();
		template<typename U, typename = std::enable_if_t<std::is_constructible_v<Result, U>>>
		Result value_or(U&& result) const;
		Error& error();
		const Result& value() const;
		const Error& error() const;

		// monadic operators
		template<class Fn>              auto map(Fn&& visitor) const;
		template<class Fn>              auto and_then(Fn&& visitor) const;
		template<class Fn, class ErrFn> auto and_then(Fn&& visitor, ErrFn&& err_visitor) const;
		template<class ErrFunc>         auto or_else(ErrFunc&& err_visitor) const;

		// operator overloads 
		explicit operator bool() const;
		Result& operator*();
		Result* operator->();
		const Result& operator*() const;
		const Result* operator->() const;
	};
}