Rust: What is the difference between ManuallyDrop and mem::forget?

1use std::mem::ManuallyDrop;
2
3let mut md = ManuallyDrop::new(vec![1, 2, 3]);
4md.push(4);  // Can still use
5unsafe { ManuallyDrop::drop(&mut md); }  // Manual drop
6
7use std::mem;
8let v = vec![1, 2, 3];
9mem::forget(v);  // Leaked, cannot access