JSON serialization of Option types as HashMap keys is not round-trippable. about rustc-serialize

[oli-obk]

this is "obsolete" right now since Options aren't allowed as hash map keys anymore.

The following test passes.

    #[test]
    fn test_encode_hashmap_with_option_key() {
        use std::io::Writer;
        use std::collections::HashMap;
        use std::fmt;
        let mut hm = HashMap::new();
        hm.insert(Some("hi"), true);
        hm.insert(None, false);
        let mut mem_buf = Vec::new();
        let mut encoder = Encoder::new(&mut mem_buf as &mut fmt::Writer);
        let result = hm.encode(&mut encoder);
        match result.err().unwrap() {
            EncoderError::BadHashmapKey => (),
            _ => panic!("expected bad hash map key")
        }
    }

I don't see how Option<String> could ever be encoded safely and trivially comprehensible. Or even Something like Option<SomeEnumWithAVariantNamedNone>.

[oli-obk]

@alexcrichton Should this be closed or should a way be found to allow this?

[alexcrichton]

Ah yes thanks @oli-obk! I think that Json just won't be able to encode all possible Rust types.