C++23 & C++26 Preview

#include <iostream>
#include <expected>
#include <string>
#include <charconv>
#include <system_error>

enum class ParseError {
    empty_input,
    invalid_format,
    out_of_range
};

std::expected<int, ParseError> parse_int(std::string_view sv) {
    if (sv.empty()) return std::unexpected(ParseError::empty_input);

    int result{};
    auto [ptr, ec] = std::from_chars(sv.data(), sv.data() + sv.size(), result);

    if (ec == std::errc::invalid_argument)
        return std::unexpected(ParseError::invalid_format);
    if (ec == std::errc::result_out_of_range)
        return std::unexpected(ParseError::out_of_range);
    if (ptr != sv.data() + sv.size())
        return std::unexpected(ParseError::invalid_format);

    return result;
}

std::expected<int, ParseError> double_if_positive(int val) {
    if (val <= 0) return std::unexpected(ParseError::out_of_range);
    return val * 2;
}

int main() {
    // Direct usage
    auto result = parse_int("42");
    if (result) {
        std::cout << "Parsed: " << *result << "\n";
    } else {
        std::cout << "Error code: " << static_cast<int>(result.error()) << "\n";
    }

    // Monadic chaining — like Rust's Result::and_then
    auto chained = parse_int("21")
        .and_then(double_if_positive)       // int -> expected<int, E>
        .transform([](int v) { return v + 1; })  // int -> int (wrapped)
        .or_else([](ParseError e) -> std::expected<int, ParseError> {
            std::cout << "Recovering from error\n";
            return 0;  // default value on error
        });

    std::cout << "Chained result: " << *chained << "\n";  // 43

    return 0;
}

#include <print>
#include <vector>
#include <string>
#include <ranges>

int main() {
    // Basic printing — no more << chains!
    std::println("Hello, {}!", "C++23");
    std::print("No newline here. ");
    std::println("But here.");

    // Formatting works just like std::format
    int x = 42;
    double pi = 3.14159;
    std::println("x = {}, pi = {:.2f}", x, pi);
    std::println("Hex: {:#x}, Binary: {:#b}", 255, 255);

    // Print to stderr
    std::println(stderr, "Warning: something happened");

    // Containers and ranges (C++23 formatter support)
    std::vector<int> v{1, 2, 3, 4, 5};
    std::println("Vector: {}", v);  // [1, 2, 3, 4, 5]

    // Formatted table
    std::println("{:<15} {:>10} {:>10}", "Name", "Score", "Grade");
    std::println("{:<15} {:>10} {:>10}", "Alice", 95, "A");
    std::println("{:<15} {:>10} {:>10}", "Bob", 87, "B+");

    return 0;
}

#include <print>
#include <ranges>
#include <vector>
#include <string>

int main() {
    std::vector<std::string> names{"Alice", "Bob", "Carol"};
    std::vector<int> scores{95, 87, 92};

    // zip — combine multiple ranges element-wise
    for (auto [name, score] : std::views::zip(names, scores)) {
        std::println("{}: {}", name, score);
    }

    std::vector<int> data{1, 2, 3, 4, 5, 6, 7, 8, 9};

    // chunk — split into groups of N
    for (auto chunk : data | std::views::chunk(3)) {
        std::print("[ ");
        for (int v : chunk) std::print("{} ", v);
        std::println("]");
    }
    // [ 1 2 3 ] [ 4 5 6 ] [ 7 8 9 ]

    // slide — sliding window of size N
    for (auto window : data | std::views::slide(3)) {
        std::print("( ");
        for (int v : window) std::print("{} ", v);
        std::println(")");
    }
    // ( 1 2 3 ) ( 2 3 4 ) ( 3 4 5 ) ... ( 7 8 9 )

    // cartesian_product — all combinations
    std::vector<char> suits{'H', 'D', 'C', 'S'};
    std::vector<int> ranks{1, 2, 3};
    for (auto [suit, rank] : std::views::cartesian_product(suits, ranks)) {
        std::print("{}{}  ", suit, rank);
    }
    std::println("");

    // enumerate — index + value (finally!)
    for (auto [i, name] : std::views::enumerate(names)) {
        std::println("[{}] {}", i, name);
    }

    return 0;
}