10 — Modern Library Types

std::optional

Use when a value may or may not exist.

std::optional<User> find_user(int id);

if (auto user = find_user(42)) {
    std::cout << user->name << '\n';
}

Avoid sentinel values like -1 or empty strings when absence is meaningful.

std::variant

Use for a value that can be one of several known types.

using Result = std::variant<int, std::string>;

Visit it:

std::visit([](const auto& value) {
    std::cout << value << '\n';
}, result);

std::any

Can hold any type, but use sparingly. It loses type clarity.

std::any value = 42;

std::string_view

A non-owning view into string data.

void print(std::string_view text) {
    std::cout << text << '\n';
}

Important: it does not own the string. Avoid returning a string_view to temporary data.

Bad:

std::string_view bad() {
    std::string s = "dead";
    return s;
}

std::span

A non-owning view over contiguous memory.

void process(std::span<int> values) {
    for (int& v : values) {
        v += 1;
    }
}

Works with vectors, arrays, and C arrays.

std::filesystem

Portable filesystem operations.

#include <filesystem>

namespace fs = std::filesystem;

for (const auto& entry : fs::directory_iterator(".")) {
    std::cout << entry.path() << '\n';
}

std::chrono

Type-safe time and duration handling.

using namespace std::chrono_literals;

auto timeout = 500ms;

Measure time:

auto start = std::chrono::steady_clock::now();
// work
auto end = std::chrono::steady_clock::now();

Quick Self-Test

You should be able to answer:

• When should you use optional?
• Why is string_view dangerous if misused?
• What problem does span solve?
• When is variant better than inheritance?
• Why use chrono instead of raw integers for time?