How Can I Use a Custom Deleter with a `std::unique_ptr` Member Variable?

Using a Custom Deleter with a std::unique_ptr Member

When working with a std::unique_ptr member in a class, there are instances where a custom deleter may be required. This is particularly relevant when the member object requires specific cleanup or destruction procedures.

Consider a scenario where your class has a member std::unique_ptr, and Bar is a third-party class with its own create() and destroy() functions. To handle the unique ownership of this member, a custom deleter can be implemented.

In a standalone function, you could utilize a std::unique_ptr with a custom deleter like so:

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

Now, let's adapt this approach to a situation where std::unique_ptr is used as a member in a class called Foo:

class Foo {
private:
    std::unique_ptr<Bar, void(*)(Bar*)> bar_;
    ...
public:
    Foo() : bar_(create(), destroy) { /* ... */ }
    // ...
};

Notice that no lambda or custom deleter is necessary in this implementation because destroy itself serves as the deleter. This allows for a clean and concise way to manage the unique ownership of the Bar member while utilizing its custom destruction procedure.

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