Challenge 3: What the vtable Is, and What It Replaces From c2-7 — Possible Solution
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The vtable is a hidden, compiler-generated table of function pointers
-- one entry per virtual function a class declares -- associated with
every class that has at least one virtual function. Every OBJECT of
such a class carries a hidden pointer to its own class's vtable (set
automatically when the object is constructed). When a virtual function
is called through a base-class pointer or reference, the compiler
generates code that follows the object's hidden vtable pointer,
looks up the correct function pointer for the function being called,
and jumps to whatever function that entry actually points to --
resolved using the OBJECT's real vtable (tied to its actual type), not
the pointer's own declared type.

The specific piece c2-7 wrote manually that the vtable now replaces:
in that chapter's own hand-rolled pattern, the Circle struct explicitly
contained its own function-pointer FIELD (`float (*area)(void *self);`),
manually assigned to point at circle_area when the struct was
initialized (`Circle c = {5.0f, circle_area};`). The PROGRAMMER was
responsible for declaring that field, remembering to populate it
correctly for every instance, and calling through it explicitly
(`c.area(&c)`). The vtable mechanism this chapter introduces is
literally the SAME shape of solution -- a per-type table of function
pointers, looked up and called through at runtime -- except the
compiler now generates the table itself (once per class, not once per
object), automatically populates every instance's hidden pointer to
it, and automatically generates the lookup-and-call code whenever a
virtual function is invoked through a base pointer -- removing every
one of the manual steps c2-7 required the programmer to get right by
hand.

WHY THIS WORKS AS AN ANSWER
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This defines the vtable's actual structure and lookup mechanism
precisely (per-class table, per-object hidden pointer, runtime lookup
tied to the object's real type), and names the SPECIFIC c2-7 artifact
being replaced (the manually-declared, manually-populated function-
pointer struct field) rather than a vague "it's like what c2-7 did."