This is usually the case for opaque pointers.

One type of opaque pointer commonly used in C++ class declarations is the d-pointer.

Read more in the article Opaque pointer.

The only thing that the client can do with an object of such a type is to take its memory address, to produce an opaque pointer.

The type is an opaque pointer to the real implementation, that is not defined in the specification.

In some languages, such as Java, the only kind of opaque type provided is the opaque pointer.

Opaque pointers are present in several programming languages including Ada, C, C++ and Modula-2.

The type system can handle any singly inherited class structure, in addition to non-classed types such as opaque pointers, strings, and variously sized integers and floating point numbers.

Opaque pointers are a way to hide the implementation details of an interface from ordinary clients, so that the implementation may be changed without the need to recompile the modules using it.

In computer programming, an opaque pointer is a special case of an opaque data type, a datatype declared to be a pointer to a record or data structure of some unspecified type.

If the language is strongly typed, programs and procedures that have no other information about an opaque pointer type T can still declare variables, arrays, and record fields of type T, assign values of that type, and compare those values for equality.

While such objects can be used in GObject by simply treating them as opaque pointers (), it is often a good idea to create a derived pointer type, documenting the fact that the pointers should reference a particular kind of object, even though nothing else is said about it.