Aggregate initialization of noncopyable base class

Question

I am constructing derived class from non-copyable base class. I would like to aggregate-initialize Base in the initializer:

// for convenience, could be any other way to disable copy
#include<boost/noncopyable.hpp>
struct Base: public boost::noncopyable{
    int a;
};
struct Derived: public Base{
    Derived(int a): Base{a} {}
};

but I am getting:

error: could not convert ‘a’ from ‘int’ to ‘boost::noncopyable_::noncopyable’

As I understand, noncopyable cannot be initialized, fair enough. Can I then somehow craft the aggregate initializer so that noncopyable initialization is skipped? (I tried e.g. things like Base{{},a} without real understanding, but that did not work either: ~noncopyable is protected).

Or will I need to explicitly define Base::Base which will skip the noncopyable initialization, using it from Derived::Derived instead of the aggregate initialization?

Answer 1

The aggregate initialization of the base class you tried

Derived(int a): Base{{}, a} {}
//                   ^^ 

Would have worked if the constructor of boost::noncopyable wasn't protected (see here).

The easiest fix should be to add a constructor to the base class.

#include <boost/core/noncopyable.hpp>

struct Base: private boost::noncopyable
{
    int a;
    Base(int a_) : a{a_} {}
};

struct Derived: public Base
{
    Derived(int a): Base{a} {}
};