struct boxed_int { f: &int, } fn get(bi: &r/boxed_int) -> &r/int { bi.f } fn with(bi: &r/boxed_int) { // Here, the upcast is allowed because the `boxed_int` type is // contravariant with respect to `&r`. See also // compile-fail/regions-infer-invariance-due-to-mutability.rs let bi: &blk/boxed_int/&blk = bi; assert *get(bi) == 22; } fn main() { let g = 22; let foo = boxed_int { f: &g }; with(&foo); }