Simple dd style command line parser

command_line.hpp

#include <map>
#include <string>
#include <algorithm>

/**
* Accepts a `dd` style (foo=bar) command line. For simplicity it has 
* no support parameter descriptions.
*/
class command_line
{
public:
	using storage_type = std::map<std::string, std::string, std::less<>>;
	using key_type = storage_type::key_type;
	using value_type = storage_type::value_type;
	using mapped_type = storage_type::mapped_type;

	explicit command_line(int argc, char** argv)
	{
		for(int k = 1; k < argc; ++k)
		{
			auto const arg = std::string_view{argv[k]};
			auto const i = std::ranges::find(arg, '=');
			if(i == std::end(arg))
			{ throw std::runtime_error{std::string{arg}.append(" is missing a value")}; }
			m_storage[std::string{std::begin(arg), i}] = std::string{i + 1, std::end(arg)};
		}
	}

	auto const& operator[](std::string_view key) const
	{
		auto i = m_storage.find(key);
		if(i == std::end(m_storage))
		{ throw std::runtime_error{std::string{"Mandatory arguemnt "}.append(key).append(" not given")}; }
		return i->second;
	}

	auto begin() const { return std::begin(m_storage); }

	auto end() const { return std::end(m_storage); }

	auto size() const { return std::size(m_storage); }

private:
	storage_type m_storage;
};