Hiding class pointers -- was it a good idea?

[Walter Bright]

Bill Baxter wrote:
> The problem I see is that it's really not always clear whether a value 
> or reference type is desired.  Currently I'm thinking about container 
> classes.  Value semantics are convenient and efficient for small 
> containers.  D's built-in containers are basically structs as is often 
> pointed out.  If you create lots of little Sets here and there you don't 
> want each Set to require two allocations (one for the object itself, and 
> another for adding some content to it).  Only one allocation is really 
> required there.  But you might also want your set to implement some 
> interfaces (a la Tango).  Then you're forced into a class even though 
> you don't particularly want anyone to subclass your Set.  And even 
> though you'd rather use it primarily as a value type (for efficiency, 
> plus since the intent is a 'final' class there will be no derived 
> classes and thus there are no slicing issues).

If you're using interfaces in a class, it's consuming 8 bytes plus 4 
bytes per interface. That means it's cheaper to pass around by reference 
than by value. I don't think you're going to see a real efficiency gain 
by adding value semantics for such cases.