cpp_optional_extras

A handful of C++ utilities I wish std::optional<T> had.

Purpose

C++17 brought us std::optional<T>, then C++23 enhanced it with a couple of member-functions (e.g. transform) to safely express common data transformations.

This library draws inspiration from other languages ​​and provides a handful of additional functions to make working with std::optional<T> even more ergonomic and less error-prone by encapsulating common patterns into reusable algorithms around correct access to the underlying T.

Examples

You have an function get_access_token that returns an access_token and you want to verify_signature and do something when it's valid. With exists:

auto get_access_token() -> std::optional<access_token>;
auto verify_signature(access_token const &) -> bool;

if (optx::exists(get_access_token(), verify_signature)) {
    // do something
}

You have a person with optional first_name and second_name, and you want to format them when both are available or return the first available one, otherwise return N/A when neither is available. With append:

struct person {
  std::optional<std::string> first_name;
  std::optional<std::string> second_name;

  auto format_name() const -> std::string {
    return optx::append(first_name, second_name,
                        [](auto const fname, auto const sname) {
                          return fname + " " + sname;
                        })
        .value_or(std::string{"N/A"});
  }
};

These are just two of the available algorithms!

Functions

• filter(optional<T>, T -> bool) -> optional<T>
• exists(optional<T>, T -> bool) -> bool
• contains(optional<T>, T) -> bool
• zip_with(optional<L>, optional<R>, (L, R) -> O) -> optional<O>
• zip(optional<L>, optional<R>) -> optional<pair<L, R>>
• unzip(optional<pair<L, R>) -> pair<optional<L>, optional<R>>
• append(optional<T>, optional<T>, (T, T) -> T) -> optional<T>
• fold(optional<T>, () -> R, T -> R) -> R

Requirements

C++20

Usage

This is a header-only library. Algorithms live in algorithm.hpp.

• (Optional) Link against the INTERFACE rvarago::optional_extras target in your CMake build.
• Include rvarago/optional_extras/algorithm.hpp
• Call into functions from the rvarago::optional_extras::algorithm namespace, perhaps alias it as namespace optx = rvarago::optional_extras::algorithm; to save keystrokes.

Contributing

This repository has a flake.nix with everything I need for development/CI (toolchain, language server, etc).

Furthermore, with:

nix develop -c check

You run all CI checks locally.