Hiding class pointers -- was it a good idea?

[Walter Bright]

Gregor Richards wrote:
> OK, OK, I guess I should respond with an argument from computer science 
> as well :)
> 
> In the normal definition of Object Orientation, an object is a means of 
> storing a context in which operations can be performed. The abstraction 
> behind this (yay we're modeling the universe in code but realistically 
> we aren't yay) is irrelevant, as fundamentally OO is just a means of 
> storing and passing contexts. Because this is a context, it makes no 
> sense whatsoever to pass it around with duplication - duplicating 
> contexts is nonsense.
> 
> structs are sort of a hack for compatibility and/or optimization. They 
> are not contexts, they are means of creating more complicated values. 
> While a "Point" could be a struct, really being a more complicated 
> value, an "NPC" would always be a class, since it is a context.
> 
> The fact that this is inconsistent with C++ is irrelevant: D is more to 
> the spirit of good OO.

You put your finger on the very good reason why polymorphic, inheritable 
types in D are restricted to being reference types, not value types. OOP 
requires this characteristic.

In C++, an OOP class can be used/misused by the user as a value type or 
a reference type, all out of the purview of the class designer. The 
class designer must control this, not the class user.