| // Issue 52126: With respect to variance, the assign-op's like += were |
| // accidentally lumped together with other binary op's. In both cases |
| // we were coercing the LHS of the op to the expected supertype. |
| // |
| // The problem is that since the LHS of += is modified, we need the |
| // parameter to be invariant with respect to the overall type, not |
| // covariant. |
| |
| use std::collections::HashMap; |
| use std::ops::AddAssign; |
| |
| pub fn main() { |
| panics(); |
| } |
| |
| pub struct Counter<'l> { |
| map: HashMap<&'l str, usize>, |
| } |
| |
| impl<'l> AddAssign for Counter<'l> |
| { |
| fn add_assign(&mut self, rhs: Counter<'l>) { |
| rhs.map.into_iter().for_each(|(key, val)| { |
| let count = self.map.entry(key).or_insert(0); |
| *count += val; |
| }); |
| } |
| } |
| |
| /// Often crashes, if not prints invalid strings. |
| pub fn panics() { |
| let mut acc = Counter{map: HashMap::new()}; |
| for line in vec!["123456789".to_string(), "12345678".to_string()] { |
| let v: Vec<&str> = line.split_whitespace().collect(); |
| //~^ ERROR `line` does not live long enough |
| // println!("accumulator before add_assign {:?}", acc.map); |
| let mut map = HashMap::new(); |
| for str_ref in v { |
| let e = map.entry(str_ref); |
| println!("entry: {:?}", e); |
| let count = e.or_insert(0); |
| *count += 1; |
| } |
| let cnt2 = Counter{map}; |
| acc += cnt2; |
| // println!("accumulator after add_assign {:?}", acc.map); |
| // line gets dropped here but references are kept in acc.map |
| } |
| } |
