std::optional::value_or(3)

💅 std::optional::value_or(3) — C++ Standard Libary bestie energy ✨

okay so bestie, this page is literally the “give me the thing or give me the fallback” icon. no cap. it’s std::optional::value_or o’clock and we’re obsessed.

🎀 NAME 🎀

std::optional::value_or - std::optional::value_or. that’s the name, that’s the vibe, periodt.

✨ Synopsis ✨

template< class U >                               (1) (since C++17)
constexpr T value_or( U&& default_value ) const&;
template< class U >                               (2) (since C++17)
constexpr T value_or( U&& default_value ) &&;

Returns the contained value if *this has a value, otherwise returns default_value.

1. Equivalent to:

bool(*this) ? **this : static_cast<T>(std::forward<U>(default_value))

2. Equivalent to:

bool(*this) ? std::move(**this) : static_cast<T>(std::forward<U>(default_value))

🌸 Parameters 🌸

• default_value — the value to use in case *this is empty. it’s the backup plan, the safety net, the “if not, then this” bestie 🫶

🦋 Type requirements 🦋

• T must meet the requirements of CopyConstructible in order to use overload (1).
• T must meet the requirements of MoveConstructible in order to use overload (2).
• U&& must be convertible to T.

ngl these are the “check yourself before you wreck yourself” rules. no vibes-based skipping, bestie 💀

🍓 Return value 🍓

The current value if *this has a value, or default_value otherwise.

🔥 Exceptions 🔥

Any exception thrown by the selected constructor of the return value T.

so if that chosen constructor of T throws, it is not being swallowed — it’s coming through, and we respect it 😭✨

🧚 Example 🧚

// Run this code

#include <cstdlib>
#include <iostream>
#include <optional>

std::optional<const char*> maybe_getenv(const char* n)
{
    if (const char* x = std::getenv(n))
        return x;
    else
        return {};
}

int main()
{
    std::cout << maybe_getenv("SHELL").value_or("(none)") << '\n';
    std::cout << maybe_getenv("MYPWD").value_or("(none)") << '\n';
}

🌈 Possible output 🌈

/usr/bin/zsh
(none)

that’s the possible output listed on the page — iconic, honestly 💖

👑 See also 👑

• value returns the contained value (public member function).

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sign-off time, bestie: this page is from http://cppreference.com, version 2024.06.10, dated 2024.06.10, for std::optional::value_or(3). slay, hydrate, and may your optionals always have a value when you need one 💜🎀