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#include <iostream>
#include <map>
#include <string>
#include <type_traits>
#include <concepts>   // C++20

// C++20 Concept: requires arithmetic type
template<typename T>
concept Numeric = std::is_arithmetic_v<T>;

// Constrained function template
template<Numeric T>
T square(T value) { return value * value; }

// if constexpr: compile-time branching inside template
template<typename T>
std::string describe(T val) {
    if constexpr (std::is_integral_v<T>)
        return "integer: " + std::to_string(val);
    else if constexpr (std::is_floating_point_v<T>)
        return "float: " + std::to_string(val);
    else
        return "other";
}

int main() {
    // Structured bindings with map iteration (C++17)
    std::map<std::string, int> inventory = {
        {"apples", 10}, {"bananas", 5}, {"cherries", 25}
    };
    for (const auto& [item, qty] : inventory)
        std::cout << item << ": " << qty << "
";

// Structured binding with pair
    auto [q, r] = std::pair{17 / 5, 17 % 5};
    std::cout << "17 / 5 = " << q << " remainder " << r << "
";

// if constexpr in template
    std::cout << describe(42)   << "
";
    std::cout << describe(3.14) << "
";

// Concepts: square only works for Numeric types
    std::cout << "square(7)   = " << square(7)   << "
";
    std::cout << "square(2.5) = " << square(2.5) << "
";
    // square("hi") would be a clear concept violation error

return 0;
}