cts like -->

<!-- `Box<Foo>`, which need to clean-up both the `Box` allocation as well as the -->

<!-- internal type when they go out of scope. The `size` and `align` fields store -->

<!-- the size of the erased type, and its alignment requirements; these are -->

<!-- essentially unused at the moment since the information is embedded in the -->

<!-- destructor, but will be used in the future, as trait objects are progressively -->

<!-- made more flexible. -->

<p>各vtableの <code>destructor</code> �