Abstract classes vs interfaces, casting from void*

kinke kinke at gmx.net
Fri Aug 9 13:19:14 UTC 2019

On Friday, 9 August 2019 at 12:26:59 UTC, John Colvin wrote:
> Why is there no "hi" between 0 and 1?

Because you are treating the unadjusted object pointer as 
interface pointer and then call the only virtual function of that 
interface, in the 2nd vtbl slot (after the TypeInfo ptr). Casting 
a class ref to an interface offsets the pointer, so that the 
interface ref points to the interface vptr for that object 
instance. This is missing in that line, and so you are invoking 
the first virtual function of class C, which is some base 
function in `Object`.

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