and
.B SodClass
is its own metaclass.
-It is not possible to define root classes because of circularities:
+It is not possible to define root classes in module files
+because of circularities:
.B SodObject
has
.B SodClass
-as its metaclass, and
+as its metaclass,
+and
.B SodClass
is a subclass of
.BR SodObject .
.IB a ;
.PP
for each of
-.IR C 's superclasses
+.IR C 's
+superclasses
.IR A
in the same chain in some (unimportant) order.
A `pointer to
.B ichain
must have as a prefix the
.B ichain
-for each superclass in the same chain, and
-each slot must be stored in exactly one place.
+for each superclass in the same chain,
+and each slot must be stored in exactly one place.
The layout of vtables doesn't have this second requirement:
it doesn't matter that there are
multiple method entry pointers
for the same effective method
as long as they all work correctly.
+Indeed, it's essential that they do,
+because each chain's method entry function
+will need to apply a different offset to the receiver pointer
+before invoking the effective method.
.PP
A vtable for a class
.I C
.fi
.PP
The outer layer is a
-.IP
.B union
.IB C __vtu_ h
-.PP
containing a member
.IP
.B struct
The metaclass
.I R
of
-.IR O .
+.I O
is then the
.I root metaclass
of
in the same chain as
.IR J .
Then, if there is currently no class pointer of type
-.I Q
+.IR Q ,
then add a member
.RS
.IP
.I A
defines any messages,
and there is currently no member
-.I a
+.IR a ,
then add a member
.RS
.IP