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// run-pass
#![feature(const_fn_union)]
#![allow(dead_code)]
#[repr(C)]
union Transmute<T: Copy, U: Copy> {
t: T,
u: U,
}
trait Bar {
fn bar(&self) -> u32;
}
struct Foo {
foo: u32,
bar: bool,
}
impl Bar for Foo {
fn bar(&self) -> u32 {
self.foo
}
}
impl Drop for Foo {
fn drop(&mut self) {
assert!(!self.bar);
self.bar = true;
println!("dropping Foo");
}
}
#[derive(Copy, Clone)]
struct Fat<'a>(&'a Foo, &'static VTable);
struct VTable {
drop: Option<for<'a> fn(&'a mut Foo)>,
size: usize,
align: usize,
bar: for<'a> fn(&'a Foo) -> u32,
}
const FOO: &dyn Bar = &Foo { foo: 128, bar: false };
const G: Fat = unsafe { Transmute { t: FOO }.u };
const F: Option<for<'a> fn(&'a mut Foo)> = G.1.drop;
const H: for<'a> fn(&'a Foo) -> u32 = G.1.bar;
fn main() {
let mut foo = Foo { foo: 99, bar: false };
(F.unwrap())(&mut foo);
std::mem::forget(foo); // already ran the drop impl
assert_eq!(H(&Foo { foo: 42, bar: false }), 42);
}
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