COM interfaces are Immutable
Interface is not allowed to change
The phrase "COM interfaces are immutable" means that once a COM interface is published or deployed, its specification is not allowed to change. This applies even if different COM objects implement that interface.
For example, once interface IX1
is published or deployed, all COM objects that implement IX1
must implement the interface exactly as specified. So if IX1
has the following IDL (interface definition language) definition:
[object,uuid(...)]
interface IX1 : IUnknown
{
HRESULT x1(int ix);
HRESULT x2();
}
[1]vtable aka virtual table: For every class that contains virtual functions, the compiler constructs a virtual table, vtable. The vtable contains an entry for each virtual function accessible by the class and stores a pointer to its definition. Only the most specific function definition callable by the class is stored in the vtable.