std::weak_ordering(3)

🦋 std::weak_ordering(3) 🦋

okay so this is the std::weak_ordering page from the C++ Standard Libary manual, and bestie we are going to get you through it 💅

💖 NAME 💖

std::weak_ordering — std::weak_ordering

✨ Synopsis ✨

Defined in header <compare>
class weak_ordering;         (since C++20)

The class type std::weak_ordering is the result type of a three-way comparison that:

• Admits all six relational operators (==, !=, <, <=, >, >=).
• Does not imply substitutability: if a is equivalent to b, f(a) may not be equivalent to f(b), where f denotes a function that reads only comparison-salient state that is accessible via the argument's public const members. In other words, equivalent values may be distinguishable.
• Does not allow incomparable values: exactly one of a < b, a == b, or a > b must be true.

🍓 Constants 🍓

The type std::weak_ordering has three valid values, implemented as const static data members of its type:

• less — inline constexpr [static] member constant: a valid value of the type std::weak_ordering indicating less-than (ordered before) relationship (public static member constant).
• equivalent — inline constexpr [static] member constant: a valid value of the type std::weak_ordering indicating equivalence (neither ordered before nor ordered after) (public static member constant).
• greater — inline constexpr [static] member constant: a valid value of the type std::weak_ordering indicating greater-than (ordered after) relationship (public static member constant).

🌈 Conversions 🌈

std::weak_ordering is implicitly-convertible to std::partial_ordering, while std::strong_ordering is implicitly-convertible to weak_ordering.

• operator partial_ordering — implicit conversion to std::partial_ordering (public member function)

💜 std::weak_ordering::operator partial_ordering 💜

constexpr operator partial_ordering() const noexcept;

Return value

std::partial_ordering::less if v is less, std::partial_ordering::greater if v is greater, std::partial_ordering::equivalent if v is equivalent.

🔥 Comparisons 🔥

Comparison operators are defined between values of this type and literal 0. This supports the expressions a <=> b == 0 or a <=> b < 0 that can be used to convert the result of a three-way comparison operator to a boolean relationship; see std::is_eq, std::is_lt, etc.

These functions are not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when std::weak_ordering is an associated class of the arguments.

💀 Undefined behavior alert: the behavior of a program that attempts to compare a weak_ordering with anything other than the integer literal 0 is undefined. Not “kinda undefined.” Not “undefined-ish.” UNDEFINED. Do not do it, bestie.

• operator==, operator<, operator>, operator<=, operator>=, operator<=> — compares with zero or a weak_ordering (function)

💅 operator== 💅

1. friend constexpr bool operator==( weak_ordering v, /*unspecified*/ u ) noexcept; (1)
2. friend constexpr bool operator==( weak_ordering v, weak_ordering w ) noexcept = default; (2)

Parameters

• v, w — std::weak_ordering values to check
• u — an unused parameter of any type that accepts literal zero argument

Return value

1. true if v is equivalent, false if v is less or greater
2. true if both parameters hold the same value, false otherwise

💅 operator< 💅

1. friend constexpr bool operator<( weak_ordering v, /*unspecified*/ u ) noexcept; (1)
2. friend constexpr bool operator<( /*unspecified*/ u, weak_ordering v ) noexcept; (2)

Parameters

• v — a std::weak_ordering value to check
• u — an unused parameter of any type that accepts literal zero argument

Return value

1. true if v is less, and false if v is greater or equivalent
2. true if v is greater, and false if v is less or equivalent

💅 operator<= 💅

1. friend constexpr bool operator<=( weak_ordering v, /*unspecified*/ u ) noexcept; (1)
2. friend constexpr bool operator<=( /*unspecified*/ u, weak_ordering v ) noexcept; (2)

Parameters

• v — a std::weak_ordering value to check
• u — an unused parameter of any type that accepts literal zero argument

Return value

1. true if v is less or equivalent, and false if v is greater
2. true if v is greater or equivalent, and false if v is less

💅 operator> 💅

1. friend constexpr bool operator>( weak_ordering v, /*unspecified*/ u ) noexcept; (1)
2. friend constexpr bool operator>( /*unspecified*/ u, weak_ordering v ) noexcept; (2)

Parameters

• v — a std::weak_ordering value to check
• u — an unused parameter of any type that accepts literal zero argument

Return value

1. true if v is greater, and false if v is less or equivalent
2. true if v is less, and false if v is greater or equivalent

💅 operator>= 💅

1. friend constexpr bool operator>=( weak_ordering v, /*unspecified*/ u ) noexcept; (1)
2. friend constexpr bool operator>=( /*unspecified*/ u, weak_ordering v ) noexcept; (2)

Parameters

• v — a std::weak_ordering value to check
• u — an unused parameter of any type that accepts literal zero argument

Return value

1. true if v is greater or equivalent, and false if v is less
2. true if v is less or equivalent, and false if v is greater

💅 operator<=> 💅

1. friend constexpr weak_ordering operator<=>( weak_ordering v, /*unspecified*/ u ) noexcept; (1)
2. friend constexpr weak_ordering operator<=>( /*unspecified*/ u, weak_ordering v ) noexcept; (2)

Parameters

• v — a std::weak_ordering value to check
• u — an unused parameter of any type that accepts literal zero argument

Return value

1. v.
2. greater if v is less, less if v is greater, otherwise v.

🌸 Example 🌸

This section is incomplete Reason: no example

🦋 See also 🦋

• strong_ordering (C++20) — the result type of 3-way comparison that supports all 6 operators and is substitutable (class)
• partial_ordering (C++20) — the result type of 3-way comparison that supports all 6 operators, is not substitutable, and allows incomparable values (class)

🎀 Category 🎀

• Todo no example

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made with 💖 from cppreference.com, page date 2024.06.10 — mwah, go slay your comparisons 🫶✨