Tuesday, February 21, 2012

subverting - multiple inheritance (my take

!! With MI, the "this" pointer field is not always identical between the Base object and the Derived object.
** Remember a primitive technique of a home-made "class" is a C struct + a self-pointer field [2]. Similarly, In Python methods, "self" must be the first argument...

[2] I don't think we should add a 32-bit field to each instance! I guess compiler can help make do without it.

!! In a Derived instance, there's not always a single Base1 instance.
** Basic example -- D extends C1 and C2, which both extend B.
** Even if C1 and C2 both virtually extend B, if C3 extends B without "virtual", D instance still embeds 2 B instances.

!! Casting within inheritance hierarchy doesn't always maintain the address held inside a Derived pointer or Base pointer. SI -- always. ARM P 221 says "with MI, casting changes the value of a pointer".

!! Each Derived instance uses more than one vtbl. If D inherits from B1 and B2, then that instance uses two vtbl's. See ARM P230.

!! AOB (see other posts) assumes a 0 "delta" but in MI, delta is introduced because it's not 0! ARM P222

-- Below rules still holds,  in SI and MI --
dtor sequence is the exact reverse of ctor sequence which is BCDC (see other posts)

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