#![feature(const_fn)] struct S { state: u32, } impl S { const fn foo(&mut self, x: u32) { self.state = x; //~^ contains unimplemented expression } } const FOO: S = { let mut s = S { state: 42 }; s.foo(3); //~ ERROR mutable references are not allowed in constants s }; type Array = [u32; { let mut x = 2; let y = &mut x; //~^ ERROR mutable references are not allowed in constants *y = 42; //~^ ERROR constant contains unimplemented expression type *y }]; fn main() { assert_eq!(FOO.state, 3); }