Declaring an "interface" in C++ and not emmiting its vtable to every translation unit

Question

According to this answer, the way to declare a class in C++ conceptually analogous to an interface is like this:

class IDemo
{
public:
    virtual ~IDemo() {}
    virtual void OverrideMe() = 0;
};

But when I do this, I get the warning: 'IDemo' has no out-of-line virtual method definitions; its vtable will be emitted in every translation unit. Is there a proper way to use such interfaces in a project without polluting every translation unit with those vtables?

Answer 1

You already have a non-pure virtual function: the destructor! Just define it in its own translation unit.

// IDemo.h

class IDemo
{
public:
    virtual ~IDemo();
    virtual void OverrideMe() = 0;
};

// IDemo.cpp

IDemo::~IDemo() = default;