rust-lang/rust — pull request #19490 by oli-obk (2014-12-03 08:11:03+00:00)
Title: libserialize: allow non string key map import/export

importing object type string key maps is still supported
writing them should be explicit, and can be done as follows

```rust
let some_tree_map : TreeMap = ...;
Json::Object(some_tree_map).to_writer(&mut writer);
```

related to #8335, #9028