How do I use a custom deleter with a std::unique_ptr member?

Question

I have a class with a unique_ptr member.

class Foo {
private:
    std::unique_ptr<Bar> bar;
    ...
};

The Bar is a third party class that has a create() function and a destroy() function.

If I wanted to use a std::unique_ptr with it in a stand alone function I could do:

void foo() {
    std::unique_ptr<Bar, void(*)(Bar*)> bar(create(), [](Bar* b){ destroy(b); });
    ...
}

Is there a way to do this with std::unique_ptr as a member of a class?

Answer 1

Assuming that create and destroy are free functions (which seems to be the case from the OP's code snippet) with the following signatures:

Bar* create();
void destroy(Bar*);

You can write your class Foo like this

class Foo {

    std::unique_ptr<Bar, void(*)(Bar*)> ptr_;

    // ...

public:

    Foo() : ptr_(create(), destroy) { /* ... */ }

    // ...
};

Notice that you don't need to write any lambda or custom deleter here because destroy is already a deleter.