Null references redux + Cyclone

[Michel Fortin]

On 2009-09-28 15:36:05 -0400, bearophile <bearophileHUGS at lycos.com> said:

> Compiled with DMD the running time seems about unchanged. I have no 
> idea why. Maybe some of you can tell me.

If I recall correctly, implementing an interface adds a variable to an 
class which contains a pointer to that interface's vtable 
implementation for that particular class. An interface pointer points 
to that variable inside the object instead (not at the beginning of the 
object allocated space), and calling a function on it involves 
dereferencing the interface's vtable, and calling the right function. 
Obtaining the real "this" pointer for calling the function involves 
looking at the first value in the interface's vtable which contains an 
offset you can substract from the interface pointer to get the object 
pointer.

So basically, if I recall well how it works, calling a function on an 
interface reference involves one more substraction than calling a 
member function a class reference, which is pretty marginal.


-- 
Michel Fortin
michel.fortin at michelf.com
http://michelf.com/