On dinsdag, feb 25, 2003, at 15:01 Europe/Brussels, Anton Tichawa wrote:
What object code is generated for this? I assume that, informally speaking,
Ord(TClassB) = Ord(@VMT)
and that
if x IS TClassB
yields somthing like
if @(x.VMT) = TClassB?
Am I wrong here?
Yes, because "is" also returns true if the instance is of a type that inherits from tclassb. So the "is" operator is translated into a call to the following helper routine
function fpc_do_is(aclass : tclass;aobject : tobject) : boolean;[public,alia
s: 'FPC_DO_IS']; {$ifdef hascompilerproc} compilerproc; {$endif}
begin
fpc_do_is:=assigned(aobject) and assigned(aclass) and
aobject.inheritsfrom(aclass);
end;
Jonas
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