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