std::regular

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Concepts library

Core language concepts same_as (C++20) derived_from (C++20) convertible_to (C++20) common_reference_with (C++20) common_with (C++20) integral (C++20) signed_integral (C++20) unsigned_integral (C++20) floating_point (C++20) swappableswappable_with (C++20)(C++20) destructible (C++20) constructible_from (C++20) default_initializable (C++20)   move_constructible (C++20) copy_constructible (C++20) assignable_from (C++20)

Comparison concepts equality_comparableequality_comparable_with (C++20)(C++20) totally_orderedtotally_ordered_with (C++20)(C++20) Object concepts movable (C++20) copyable (C++20) semiregular (C++20) regular (C++20) Callable concepts invocableregular_invocable (C++20)(C++20) predicate (C++20) relation (C++20) equivalence_relation (C++20) strict_weak_order (C++20)

Exposition-only concepts boolean-testable  (C++20)

 

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