No op delete for unique_ptr

Question

What would be the most concise way to pass unique_ptr a custom deleter that does nothing? I need for a JNI function I'm writing, where the C++ side expects a unique_ptr, BUT, I don't want the object held by the unique_ptr to be deleted upon exiting the JNI function - I take care of the deletion later. So I'd like to do something like:

std::unique_ptr<MyClass, noop_delete> ptr;

In one line - not with a separate function definition :-)

Answer 1

As @101010 pointed out, that's very strange to have a std::unique_ptr with a nop deleter, since the only valuable thing std::unique_ptr has is actually the deleter. Also, you said that "C++ side expects a unique_ptr", but a std::unique_ptr with a different deleter would be a different type, and this may not work.

Nevertheless, here's the way to do it:

struct nop
{
    template <typename T>
    void operator() (T const &) const noexcept { }
};

template <typename T>
using nop_unique_ptr = std::unique_ptr<T, nop>;

Note that this nop type can be used as no-operation anywhere in place of a one-argument functor.