V-tables differences between Rust and C

[Michael-F-Bryan]

@arnie

Is my understanding correct that the layout of Rust vtable is similar to this pic:

I would draw it like this:

&dyn Foo (Trait Object)
+--------+----------+
| Data * | Vtable * |
+--------+----------+
    |        |
    |        v
    |     +---------------+--------+----------+-------+
    |     | drop_in_place | size   | method_1 | ...   |
    |     +---------------+--------+----------+-------+
    v
+---------+---------+--------+
| field_1 | field_2 | ...    |
+---------+---------+--------+

And the C++ version:

Foo* (Pointer to derived object)
    |
    v
+--------+---------+---------+--------+
| Vtable*| field_1 | field_2 | ...    |
+--------+---------+---------+--------+
    |
    v
+----------+-----+
| method_1 | ... |
+----------+-----+