std::partial_order(3)

💖 NAME 💖

std::partial_order — std::partial_order

okay bestie, this is the std::partial_order(3) page from the C++ Standard Libary, and we're about to make partial ordering make sense fr fr 💅

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✨ Synopsis ✨

Defined in header <compare> — yes, that's the header, no cap.

inline namespace /* unspecified */ {

    inline constexpr /* unspecified */ partial_order = /* unspecified
(since C++20)
*/;

}

🌟 Call signature 🌟

template< class T, class U >

    requires /* see below */
constexpr std::partial_ordering

    partial_order( T&& t, U&& u ) noexcept(/* see below */);

Compares two values using 3-way comparison and produces a result of type std::partial_ordering.

Let t and u be expressions and T and U denote decltype((t)) and decltype((u)) respectively, std::partial_order(t, u) is expression-equivalent to:

• If std::is_same_v<std::decay_t<T>, std::decay_t<U>> is true:
  • std::partial_ordering(partial_order(t, u)), if it is a well-formed expression with overload resolution performed in a context that does not include a declaration of std::partial_order,
  • otherwise, std::partial_ordering(std::compare_three_way()(t, u)), if it is well-formed,
  • otherwise, std::partial_ordering(std::weak_order(t, u)), if it is well-formed.
• In all other cases, the expression is ill-formed, which can result in substitution failure when it appears in the immediate context of a template instantiation.

💅 Customization point objects 💅

The name std::partial_order denotes a customization point object, which is a const function object of a literal semiregular class type. For exposition purposes, the cv-unqualified version of its type is denoted as __partial_order_fn.

All instances of __partial_order_fn are equal. The effects of invoking different instances of type __partial_order_fn on the same arguments are equivalent, regardless of whether the expression denoting the instance is an lvalue or rvalue, and is const-qualified or not (however, a volatile-qualified instance is not required to be invocable). Thus, std::partial_order can be copied freely and its copies can be used interchangeably.

Given a set of types Args..., if std::declval<Args>()... meet the requirements for arguments to std::partial_order above, __partial_order_fn models

• std::invocable<__partial_order_fn, Args...>,
• std::invocable<const __partial_order_fn, Args...>,
• std::invocable<__partial_order_fn&, Args...>, and
• std::invocable<const __partial_order_fn&, Args...>.

Otherwise, no function call operator of __partial_order_fn participates in overload resolution.

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🧪 Example 🧪

This section is incomplete

Reason: no example

bestie there is literally no example here 😭 the page said so, not me

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👀 See also 👀

• partial_ordering (C++20) — the result type of 3-way comparison that supports all 6 operators, is not substitutable, and allows incomparable values (class)
• strong_order (C++20) — performs 3-way comparison and produces a result of type std::strong_ordering (customization point object)
• weak_order (C++20) — performs 3-way comparison and produces a result of type std::weak_ordering (customization point object)
• compare_partial_order_fallback (C++20) — performs 3-way comparison and produces a result of type std::partial_ordering, even if operator<=> is unavailable (customization point object)

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🏷️ Category: 🏷️

• Todo no example

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page sauce: http://cppreference.com · 2024.06.10 · std::partial_order(3) — bye bestie, go compare something 💖✨