error[E0594]: cannot assign to data in an index of `HashMap<u32, u32>`
  --> $DIR/hashmap-index-mut.rs:5:5
   |
LL |     map[&0] = 1;
   |     ^^^^^^^^^^^ cannot assign
   |
   = help: trait `IndexMut` is required to modify indexed content, but it is not implemented for `HashMap<u32, u32>`
help: use `.insert()` to insert a value into a `HashMap<u32, u32>`, `.get_mut()` to modify it, or the entry API for more flexibility
   |
LL -     map[&0] = 1;
LL +     map.insert(&0, 1);
   |
LL -     map[&0] = 1;
LL +     if let Some(val) = map.get_mut(&0) { *val = 1; };
   |
LL -     map[&0] = 1;
LL +     let val = map.entry(&0).or_insert(1);
   |

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0594`.