Variadic Template Exercise

concatenate_strings_challenge.cpp

// Challenge: Concatenate Strings
// This coding challenge involves creating a C++ class template called strOps.
// The goal is to concatenate a variable number of strings using variadic
// templates and fold expressions, count the total number of characters in the
// concatenated string, and keep track of the total number of input strings.

// Key Concepts:
// 1. Utilizing variadic templates to accept a variable number of input strings.
// 2. Implementing fold expressions to efficiently concatenate strings.
// 3. Utilizing variadic variable templates to count the total number of input
// strings.
// 4. Designing a class template with member functions to access the
// concatenated string, its length, and the count of input strings.
// 5. Creating a separate variadic function template (display_info) to display
// information about the concatenated string, character count, and string count.

// https://godbolt.org/z/G5chdPdGT

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

template <typename... Strings>
class strOps {
   public:
    // Constructor to concatenate strings and calculate information
    explicit strOps(const Strings &...strings)
        : concatenated_(concatenate(strings...)),
          total_characters_(count_characters(concatenated_)) {}

    std::string get_string() const { return concatenated_; }

    std::size_t get_string_length() const { return total_characters_; }

    std::size_t get_count() const { return total_strings_; }

   private:
    std::string concatenated_;
    std::size_t total_characters_;
    std::size_t total_strings_ =
        count_<Strings...>;  // sizeof...(Strings) is another option

    // Counts total strings using variadic variable template
    template <typename... T>
    static constexpr std::size_t count_ =
        (std::is_same_v<T, std::string> + ...);

    // Helper function to concatenate strings using fold expression
    template <typename... Args>
    std::string concatenate(const Args &...args) const {
        return (args + ...);
    }

    // Helper function to count total characters in a string
    std::size_t count_characters(std::string_view sv) const {
        return sv.length();
    }
};

// Variadic function template to display information
template <typename... Ts>
void display_info(Ts... ts) {
    ((std::cout << ts), ...) << '\n';
}

int main() {
    strOps<std::string, std::string, std::string, std::string, std::string>
        strConcatenator("Hello ", "world", " in C++",
                        " template metaprogramming", "!");
    display_info("String: ", strConcatenator.get_string());
    display_info("Total characters: ", strConcatenator.get_string_length());
    display_info("Number of strings merged: ", strConcatenator.get_count());
    return 0;
}