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Defined in header <concepts> | ||
template<class T> concept semiregular=std::copyable<T>&&std::default_initializable<T>; | (since C++20) | |
Thesemiregular concept specifies that a type is both copyable and default constructible. It is satisfied by types that behave similarly to built-in types likeint, except that they need not support comparison with==.
#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; => assignmentstruct 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::semiregularauto 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:
444
(C++20) | specifies that a type is regular, that is, it is bothsemiregular andequality_comparable(concept)[edit] |
