Use inheriting constructors to import constructors into a derived class that does not need further explicit initialization

Reason

If you need those constructors for a derived class, re-implementing them is tedious and error-prone.

Example

std::vector has a lot of tricky constructors, so if I want my own vector, I don't want to reimplement them:

class Rec {
    // ... data and lots of nice constructors ...
};

class Oper : public Rec {
    using Rec::Rec;
    // ... no data members ...
    // ... lots of nice utility functions ...
};

Example, bad

struct Rec2 : public Rec {
    int x;
    using Rec::Rec;
};

Rec2 r {"foo", 7};
int val = r.x;   // uninitialized

Enforcement

Make sure that every member of the derived class is initialized.

C.copy: Copy and move

Concrete types should generally be copyable, but interfaces in a class hierarchy should not. Resource handles might or might not be copyable. Types can be defined to move for logical as well as performance reasons.