std::experi...al::optional(3)

💖 std::experi...al::optional(3) 💖

okay bestie, welcome to the constructor page for std::experimental::optional::optional, from the C++ Standard Libary (the header literally spells it “Libary” and we are keeping that detail because facts are sacred 💀). This is all about making an optional that either holds a value or is empty, and the overloads are giving “pick your fighter” energy. ✨

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💖 NAME 💖

std::experimental::optional::optional — std::experimental::optional::optional

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✨ Synopsis ✨

Every overload here is tagged (library fundamentals TS) in the source, and the overload numbers are basically the group-chat receipts:

constexpr optional() noexcept;
constexpr optional( std::experimental::nullopt_t ) noexcept;        (1)
optional( const optional& other );                                  (2)
optional( optional&& other ) noexcept(/* see below */);             (3)
constexpr optional( const T& value );                               (4)
constexpr optional( T&& value );                                    (5)
template< class... Args >
constexpr explicit optional( std::experimental::in_place_t, Args&&... args );  (6)
template< class U, class... Args >
constexpr explicit optional( std::experimental::in_place_t, std::initializer_list<U> ilist, Args&&... args );  (7)

Constructs a new optional object. 🎀

1. Constructs the object that does not contain a value. (empty vibe, no notes)
2. Copy constructor: If other contains a value, initializes the contained value as if direct-initializing (but not direct-list-initializing) an object of type T with the expression *other. If other does not contain a value, constructs an object that does not contain a value.
3. Move constructor: If other contains a value, initializes the contained value as if direct-initializing (but not direct-list-initializing) an object of type T with the expression std::move(*other) and does not make other empty: a moved-from optional still contains a value, but the value itself is moved from. If other does not contain a value, constructs an object that does not contain a value. This one is lowkey important, bestie.
4. Constructs an optional object that contains a value, initialized as if direct-initializing (but not direct-list-initializing) an object of type T with the expression value. This constructor is constexpr if the constructor of T selected by direct-initialization is constexpr.
5. Constructs an optional object that contains a value, initialized as if direct-initializing (but not direct-list-initializing) an object of type T with the expression std::move(value). This constructor is constexpr if the constructor of T selected by direct-initialization is constexpr.
6. Constructs an optional object that contains a value, initialized as if direct-initializing (but not direct-list-initializing) an object of type T from the arguments std::forward<Args>(args)....
7. Constructs an optional object that contains a value, initialized as if direct-initializing (but not direct-list-initializing) an object of type T from the arguments ilist, std::forward<Args>(args).... The function does not participate in overload resolution if std::is_constructible<T, std::initializer_list<U>&, Args&&...>::value != true. that != true is doing a whole lot, okay

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🌸 Parameters 🌸

• other — another optional object whose contained value to copy 🫶
• value — value to initialize the contained value with ✨
• args... — arguments to initialize the contained value with 💅
• ilist — initializer list to initialize the contained value with 🎀

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🦋 Type requirements 🦋

• T must meet the requirements of CopyConstructible in order to use overloads (2,4).
• T must meet the requirements of MoveConstructible in order to use overloads (3,5).

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🔥 Exceptions 🔥

• (2) — Throws any exception thrown by the constructor of T.
• (3) — Throws any exception thrown by the constructor of T. Has the following noexcept declaration:

noexcept(std::is_nothrow_move_constructible<T>::value)

• (4-7) — Throws any exception thrown by the constructor of T.

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🎀 Example 🎀

// Run this code

#include <experimental/optional>
#include <iostream>
#include <string>

int main()
{
    std::experimental::optional<int> o1,      // empty
                                     o2 = 1,  // init from rvalue
                                     o3 = o2; // copy-constructor

    std::experimental::optional<std::string>
o4(std::experimental::in_place,
                                                {'a', 'b', 'c'});

    std::cout << *o2 << ' ' << *o3 << ' ' << *o4 << '\n';
}

🍓 Output 🍓

1 1 abc

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💅 See also 💅

• make_optional — creates an optional object (function template).

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🌈 Categories 🌈

• Noindexed pages
• conditionally noexcept

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mwah 💋 — source/version http://cppreference.com, dated 2024.06.10, page std::experi...al::optional(3). bye bestie 🫶