use std::fmt; struct Number { n: i64 } impl fmt::Display for Number { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "{}", self.n) } } struct List { list: Vec<Box<dyn ToString + 'static>> } impl List { fn push(&mut self, n: Box<dyn ToString + 'static>) { self.list.push(n); } } fn main() { let n: Box<_> = Number { n: 42 }.into(); let mut l: Box<_> = List { list: Vec::new() }.into(); l.push(n); let x = n.to_string(); //~^ ERROR: borrow of moved value: `n` }