760: Mainline

One possible, albeit bad, way to make the link member variables and constructor accessible is as follows:

• Put the member variables and the constructor in the protected portion of the class definition, instead of in the private portion.
• Make the header class a subclass of the link class.

*-----------------------*                 *-------------------------* 
| header                |                 | link                    | 
|                       |                 |                         | 
|   *-----------------* |    Access       |   *-------------------* | 
|   | Public portion  | |    permitted    |   | Protected portion | | 
|   |               ---------------------------->                 | |   
|   |                 | |                 |   |                   | | 
|   *-----------------* |                 |   *-------------------* | 
*-----------------------*                 *-------------------------* 
            |                                   ^  
            |                       Superclass  | 
            *-----------------------------------* 

The reason this way to enable access is a bad one is that header objects are not specialized link objects. Accordingly, to construe one class as a derived class and the other as its base class would be bad conceptually. It would be bad practically as well, for then header objects would carry around element_pointer and next_link_pointer member variables as excess baggage.