What is the purpose of the `alloc_ref_dynamic` SIL instruction?

Could some one show me example Swift code that would lead to the usage of alloc_ref_dynamic instruction in SIL?

alloc_ref_dynamic allocates an object based on a dynamic type value. It usually gets emitted in ObjC bridging thunks for initializers, since an Objective-C -init method can be called on arbitrary subclasses.