std::is_final(3)

💖 std::is_final(3) — C++ Standard Library, bestie 🎀✨

Okay so this is the manual page for std::is_final in the C++ Standard Library, and it’s giving “tiny trait, huge main character energy.” 💅

🌸 NAME 🌸

std::is_final — literally the trait that checks whether a type is final. That’s the whole name, no cap. 💖

✨ Synopsis ✨

Defined in header <type_traits>.

template< class T >              (since C++14)
struct is_final;

std::is_final is a UnaryTypeTrait.

If T is a final class, it provides the member constant value equal true. For any other type, value is false.

⚠️ If T is an incomplete class type, the behavior is undefined. Not a vibe. 💀

⚠️ If the program adds specializations for std::is_final or std::is_final_v (since C++17), the behavior is undefined. Do not do this, bestie. 🙈

🧚 Template parameters 🧚

• T — a type to check.

🌈 Helper variable template 🌈

template< class T >                                     (since C++17)
inline constexpr bool is_final_v = is_final<T>::value;

🧬 Inherited from std::integral_constant 🧬

This trait inherits from std::integral_constant, iykyk. ✨

👑 Member constants 👑

• value — true if T is a final class type, false otherwise. [static] (public static member constant).

💅 Member functions 💅

• operator bool — converts the object to bool, returns value (public member function).
• operator() — returns value (C++14) (public member function).

🦋 Member types 🦋

• value_type — bool.
• type — std::integral_constant<bool, value>.

📝 Notes 📝

std::is_final is introduced by the resolution of LWG issue 2112.

A union can be declared final (and std::is_final will detect that), even though unions cannot be used as bases in any case. That’s right, bestie: final union? Iconic. 🫶

Feature-test macro vibes:

• __cpp_lib_is_final — value 201402L, std (C++14), feature std::is_final.

🍓 Example 🍓

// Run this code

#include <type_traits>

class A {};
static_assert(std::is_final_v<A> == false);

class B final {};
static_assert(std::is_final_v<B> == true);

union U final
{
    int x;
    double d;
};
static_assert(std::is_final_v<U> == true);

int main()
{
}

🌸 See also 🌸

• is_class — checks if a type is a non-union class type (C++11) (class template).
• is_polymorphic — checks if a type is a polymorphic class type (C++11) (class template).

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💌 source/version/date: http://cppreference.com · 2024.06.10 · this manual page is std::is_final(3). mwah 💋