Possible way to achieve lazy loading with const objects

[Marco Leise]

Am 29.09.2011, 10:12 Uhr, schrieb Peter Alexander  
<peter.alexander.au at gmail.com>:

> Why would a car be able mutate it's vendor?

A car is a passive object, that's obvious. Of course it doesn't mutate the  
vendor and if it did, *mutate* doesn't mean the vendor can be robbed by  
the car or something. The vendor class still has it's encapsulation and  
invariants.

My point here is, that it is just the straight forward way to get that  
information about a car. The vendor itself doesn't need to have a  
reference to the car any more. It comes handy if I look at the car of my  
neighbor and want to buy from the same vendor who's address is printed on  
the license plate. The fastest way to implement that in a computer is a  
simple mutable pointer. Mutable, because when I buy from the vendor it has  
to change it's internal state.

The next best solution I can imagine is an external meta data table for  
cases like this. It would be a hash map that holds a CarMetaData struct  
for each car pointer with whatever is not part of the state of a car in  
the close sense.