60 lines
2.0 KiB
Rust
60 lines
2.0 KiB
Rust
|
// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
|
||
|
|
// file at the top-level directory of this distribution and at
|
||
|
|
// http://rust-lang.org/COPYRIGHT.
|
||
|
|
//
|
||
|
|
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
|
||
|
|
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
|
||
|
|
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
|
||
|
|
// option. This file may not be copied, modified, or distributed
|
||
|
|
// except according to those terms.
|
||
|
|
|
||
|
|
// 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 times 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
|
||
|
|
}
|
||
|
|
}
|