Quick Q: Uses of destructor = delete;
Quick A: If you have an object which should never, ever be deleted or stored on the stack (automatic storage), or stored as part of another object, =delete will prevent all of these.
Recently on SO:
Uses of destructor = delete;
struct Handle { ~Handle()=delete; }; struct Data { std::array<char,1024> buffer; }; struct Bundle: Handle { Data data; }; using bundle_storage = std::aligned_storage_t<sizeof(Bundle), alignof(Bundle)>; std::size_t bundle_count = 0; std::array< bundle_storage, 1000 > global_bundles; Handle* get_bundle() { return new ((void*)global_bundles[bundle_count++]) Bundle(); } void return_bundle( Handle* h ) { Assert( h == (void*)global_bundles[bundle_count-1] ); --bundle_count; } char get_char( Handle const* h, std::size_t i ) { return static_cast<Bundle*>(h).data[i]; } void set_char( Handle const* h, std::size_t i, char c ) { static_cast<Bundle*>(h).data[i] = c; }Here we have opaque Handles which may not be declared on the stack nor dynamically allocated. We have a system to get them from a known array.
I believe nothing above is undefined behavior; failing to destroy a Bundle is acceptable, as is creating a new one in its place.
And the interface doesn't have to expose how Bundle works. Just an opaque Handle.
Now this technique can be useful if other parts of the code need to know that all Handles are in that specific buffer, or their lifetime is tracked in specific ways. Possibly this could also be handled with private constructors and friend factory functions.
