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Parameter Packing and Varadic Templates ​

String concatenation with varadic templates

c++
template <std::string_view const&... Args>

class Concat {
public:

static constexpr auto impl() noexcept {
	constexpr std::size_t len = (Args.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(Args), ...);
	arr[len] = 0;

	return arr;
}

// Give the joined string static storage
static constexpr auto arr = impl();

// View as a std::string_view
static constexpr std::string_view value {arr.data(), arr.size() - 1};
};

template <std::string_view const&... Args>
static constexpr auto concat = Concat<Args...>::value;

constexpr std::string_view OUTPUT = concat<STR1,STR2,STR3>;
template <std::string_view const&... Args>

class Concat {
public:

static constexpr auto impl() noexcept {
	constexpr std::size_t len = (Args.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(Args), ...);
	arr[len] = 0;

	return arr;
}

// Give the joined string static storage
static constexpr auto arr = impl();

// View as a std::string_view
static constexpr std::string_view value {arr.data(), arr.size() - 1};
};

template <std::string_view const&... Args>
static constexpr auto concat = Concat<Args...>::value;

constexpr std::string_view OUTPUT = concat<STR1,STR2,STR3>;

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