std::semiregular - cppreference.com (original) (raw)
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 ==.
[edit] Example
#include
#include
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 myInt1{4}; // aggregate initialization: myInt1.value = 4
Single myInt2(myInt1); // copy constructor
Single myInt3; // default constructor
myInt3 = myInt2; // copy assignment operator
// myInt1 == myInt2; // Error: operator== is not defined
print(myInt1); // ok: Single is a semiregular type
print(myInt2);
print(myInt3);
} // Single variables are destroyed here
Output:
[edit] 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]