Making inheritance less tedious

[Sean Kelly]

Kristian Kilpi wrote:
> 
> I think class inheritance is a bit(?) tedious sometimes (that is, 
> unnecessarily tedious).
> (I leave interfaces out of this discussion.) 'Problems', IMHO, with it are:
> 
> 1) You cannot inherit constructors.

Consider:

     module A;

     class Pet
     {
         this( char[] name )
         {
             m_name = name;
         }

     private char[] m_name;
     }

     module B;
     import A;

     class Puppy : Pet {}
     class Aibo  : Pet {} /* arguably a pet */

Assuming the ctor is inherited, then so far so good.  Puppies and Aibos 
both have names.  Now let's say the base class has some new 
functionality added:

     class Pet
     {
         this( char[] name, Food eats )
         {
             m_name = name;
         }

     private char[] m_name;
     private Food   m_eats;
     }

The new inherited behavior makes sense for Puppies, but not necessarily 
for Aibos.  One might argue that a refactoring of the hierarchy is a 
good idea here, or that Aibos aren't actually pets, but I think it's 
reasonable to assume that because inheritance suggests specialization, 
it may occasionally be desirable to place constraints on inherited 
attributes.  Forcing the programmer to implement ctors for a class is a 
one simple way to avoid subtly breaking behavior from changes up the 
inheritance tree.


Sean