Re: C++ virtual function calls

Joe Orost <joe@sanskrit.ho.att.com> wrote:
>I don't think it is legal to hoist the virtual function lookup
>out of the loop:
>
>for( ...) {
> p->virt_func();
>}
>
>because "p" is passed to virt_func as "this", and therefore the
>function could change the subtype of "p", causing a different
>function to be called next time around the loop!


How? The virt_func cannot change the p pointer (since the address
'this' is passed by value, not by reference), and it cannot
change the type of *p (or any of its sub-objects), since the only
time objects change type in C++ is as they are being constructed
or destroyed.


--Per Bothner
Cygnus Support bothner@cygnus.com
--

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