When inheriting from a class, if you need to inherit its constructors without additional initialization you should prefer
using-declaration to inherit all base class’s constructors instead of writing them by hand.
using-declaration for inheriting constructor is a C++11 feature that makes all constructors of the base visible to the overload
resolution when initializing the derived class.
If you need to change the accessibility of one of the inherited constructors, you can do it by keeping the using-declaration and
declaring that constructor explicitly as private:
class Base {
public:
Base(int p) {}
Base(int p1, int p2) {}
};
class Derived : public Base {
using Base::Base;
Derived(int p1, int p2); // Changes constructor to private accessibility
};
int f(){
Derived b(1); // Base(int p) is visible when initializing the derived class
Derived b1(1,2); // Compilation error: Base(int p1, int p2) is not visible when initializing the derived class
}
This rule raises an issue when a constructor inherits the base class constructor without requiring any additional initialization.
Noncompliant code example
class Base {
public:
Base(int p) {}
};
class Derived : public Base {
public:
Derived(int p) : Base(p) {} // Noncompliant
};
Compliant solution
class Base {
public:
Base(int p) {}
};
class Derived : public Base {
using Base::Base;
};
