Structs' fields should be serialized in lexicographical order

[gsomix]

Structs are encoded as dictionaries, so fields' names (keys) should be serialized in the in lexicographical order. In accordance with specification:

For each possible (complex) value, there is only a single valid 1coding; i.e. there is a bijection between values and their encodings.
...
A dictionary is encoded as d<contents>e. The elements of the dictionary are 1coded each key immediately followed by its value. All keys must be byte strings and must appear in lexicographical order.

[humb1t]

@gsomix thanks, will fix the order. What about only a single valid coding, I don't think we can reach it for all languages. This guarantee works well only for theoretical types described in spec.

[humb1t]

contain-rs/linked-hash-map#48
serde-rs/serde#269
serde-rs/json#80
serde-rs/serde#65 (comment)

[humb1t]

impl<'a> ser::SerializeMap for &'a mut Serializer and impl<'a> ser::SerializeStruct for &'a mut Serializer { should preserve order.
To do so - we need to add more fields to Serializer struct and "flush" into result string in the end of the struct (e char)

[humb1t]

https://github.com/serde-rs/json - Compound type should be used