#![allow(dead_code, deprecated, unused_variables, unused_mut)] use std::fmt; struct Foo(Vec); impl fmt::Debug for Foo { fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result { fmt.debug_list().entries(self.0.iter()).finish() } } fn main() { assert_eq!(format!("{:?}", Foo(vec![10, 11])), "[10, 11]"); }