std::semiregular(3)

🌸 NAME 🌸

std::semiregular — std::semiregular. (Yes bestie, that's the whole name. It ate and left no crumbs. 🍓)

okay so you're on the std::semiregular(3) page from the C++ Standard Libary — that's the spelling in the source, don't come for me 😭 — and we're about to make this concept make sense. 🫶

✨ Synopsis ✨

Defined in header <concepts>:

template< class T >
concept semiregular = std::copyable<T> &&
std::default_initializable<T>;

(since C++20) — yes, it's that era. 💅

The semiregular concept specifies that a type is both copyable and default constructible. It is satisfied by types that behave similarly to built-in types like int, except that they need not support comparison with ==. No cap, that's the whole requirement. 🌈

🎀 Example 🎀

// Run this code

#include <concepts>
#include <iostream>

template<std::semiregular T>
// Credit Alexander Stepanov
// concepts are requirements on T
// Requirement on T: T is semiregular
// T a(b); or T a = b; => copy constructor
// T a; => default constructor
// a = b; => assignment
struct Single
{
    T value;
    // Aggregation initialization for Single behaves like following constructor:
    // explicit Single(const T& x) : value(x) {}

    // Implicitly declared special member functions behave like following definitions,
    // except that they may have additional properties:
    // Single(const Single& x) : value(x.value) {}
    // Single() {}
    // ~Single() {}
    // Single& operator=(const Single& x) { value = x.value; return *this; }
    // comparison operator is not defined; it is not required by `semiregular` concept
    // bool operator==(Single const& other) const = delete;
};

void print(std::semiregular auto x)
{
    std::cout << x.value << '\n';
}

int main()
{
    Single<int> myInt1{4};      // aggregate initialization: myInt1.value = 4
    Single<int> myInt2(myInt1); // copy constructor
    Single<int> myInt3;         // default constructor
    myInt3 = myInt2;            // copy assignment operator
//  myInt1 == myInt2;           // Error: operator== is not defined

    print(myInt1); // ok: Single<int> is a `semiregular` type
    print(myInt2);
    print(myInt3);

}   // Single<int> variables are destroyed here

⭐ Output ⭐

4
4
4

👑 See also 👑

• regular — specifies that a type is regular, that is, it is both semiregular and equality_comparable (C++20) (concept). iconique. 💅

okay that's the page, bestie 🫶 — source/version/date tea: http://cppreference.com, 2024.06.10, and the page is std::semiregular(3). byeeee 💋