# std::regular

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< cpp‎ | concepts

Defined in header `<concepts>` |  |
template< class T > concept regular = std::semiregular <T> && std::equality_comparable <T>; |  | (since C++20)

The `regular` concept specifies that a type is regular, that is, it is copyable, default constructible, and equality comparable. It is satisfied by types that behave similarly to built-in types like int, and that are comparable with `==`.

### Example

Run this code

    #include <concepts>
    #include <iostream>

    template<std::regular T>
    struct Single
    {
        T value;
        friend bool operator==(const Single&, const Single&) = default;
    };

    int main()
    {
        Single<int> myInt1{4};
        Single<int> myInt2;
        myInt2 = myInt1;

        if (myInt1 == myInt2)
            std::cout << "Equal\n";

        std::cout << myInt1.value << ' ' << myInt2.value << '\n';
    }

Output:

    Equal
    4 4

### References

- C++23 standard (ISO/IEC 14882:2024):

  - 18.6 Object concepts [concepts.object]

- C++20 standard (ISO/IEC 14882:2020):

  - 18.6 Object concepts [concepts.object]

### See also

semiregular (C++20) | specifies that an object of a type can be copied, moved, swapped, and default constructed (concept)

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