custom concat for strings and string_views

concat.cpp

#include <iostream>
#include <string>
#include <string_view>

namespace impl {
    
template<typename T>
concept StringLike = requires(T t) {
    { t.data() } -> std::convertible_to<const char*>;
    { t.size() } -> std::convertible_to<std::size_t>;
};

template<StringLike T>
size_t totalSize(const T& s) {
    return s.size();
}

template <size_t N>
size_t totalSize(const char(&)[N]) {
    return N - 1; // Exclude the null terminator
}

template <typename First, typename... Rest>
size_t totalSize(const First& first, const Rest&... rest) {
    return totalSize(first) + totalSize(rest...);
}

template <StringLike T>
void concatHelper(std::string& result, const T& arg) {
    result.append(arg.data(), arg.size());
}

template <size_t N>
void concatHelper(std::string& result, const char(&arg)[N]) {
    result.append(arg, N - 1);
}

} // namespace impl

// Accepts literals and any stirng-like objects
template <typename... Args>
std::string concat(const Args&... args) {
    std::string result;
    result.reserve(impl::totalSize(args...));  // Reserve necessary space in advance
    (impl::concatHelper(result, args), ...);  // Unpack and concatenate each argument
    return result;
}


int main() {
    std::string str1 = "Hello, ";
    std::string_view strView = "World ";
    std::string str2 = " and ";

    std::string concatenated = concat(str1, strView, "C++", str2, "programmers!");
    std::cout << concatenated << std::endl; // Outputs: Hello, World C++ and programmers!

    return 0;
}