Uses of destructor = delete;

Question

Consider the following class:

struct S { ~S() = delete; };

Shortly and for the purpose of the question: I cannot create instances of

Answer 1

Why mark a destructor as delete?

To prevent the destructor from being invoked, of course ;)

What are the use cases?

I can see at least 3 different uses:

1. The class should never be instantiated; in this case I would also expect a deleted default constructor.
2. An instance of this class should be leaked; for example, a logging singleton instance
3. An instance of this class can only be created and disposed off by a specific mechanism; this could notably occur when using FFI

To illustrate the latter point, imagine a C interface:

struct Handle { /**/ };

Handle* xyz_create();
void xyz_dispose(Handle*);

In C++, you would want to wrap it in a unique_ptr to automate the release, but what if you accidentally write: unique_ptr? It's a run-time disaster!

So instead, you can tweak the class definition:

struct Handle { /**/ ~Handle() = delete; };

and then the compiler will choke on unique_ptr forcing you to correctly use unique_ptr instead.