Deserialize object/map while maintaining order

[calebmer]

Is there a way to deserialize a map (like a JSON or YAML object) while maintaining the order of key/value pairs? The BTreeMap type deserializes into kind of what I want except it does not maintain order.

Deserializing a map to Vec<(K, V)> would be perfect.

[dtolnay]

Using an ordered map type would be more appropriate than Vec<(K, V)>. I found a linked hash map implementation and made a PR to add Serde support: contain-rs/linked-hash-map#48

LinkedHashMap will work for JSON but unfortunately not for serde-yaml because serde-yaml uses yaml_rust which uses a BTreeMap for maps.

[dtolnay]

I made a PR that adds a preserve_order feature to yaml-rust: chyh1990/yaml-rust#16. Once that merges and yaml-rust does a 0.3.1 release, I can update serde-yaml to depend on it: dtolnay/serde-yaml#14.

I will check off the PRs as they merge:

• Serde support contain-rs/linked-hash-map#48
• 0.0.10 release of linked-hash-map
• Add preserve_order feature to use LinkedHashMap instead of BTreeMap chyh1990/yaml-rust#16
• 0.3.2 release of yaml-rust
• Preserve order of map keys dtolnay/serde-yaml#14

[calebmer]

Awesome, thanks so much! If you need anything from me feel free to ask 😊
On Sun, Mar 20, 2016 at 02:06 David Tolnay notifications@github.com wrote:

I made a PR that adds a preserve_order feature to yaml-rust:
chyh1990/yaml-rust#16 chyh1990/yaml-rust#16.
Once that merges and yaml-rust does a 0.3.1 release, I can update
serde-yaml to depend on it: dtolnay/serde-yaml#14
dtolnay/serde-yaml#14.

I will check off the PRs as they merge:

• Serde support contain-rs/linked-hash-map#48
  Serde support contain-rs/linked-hash-map#48
• Add preserve_order feature to use LinkedHashMap instead of BTreeMap chyh1990/yaml-rust#16 Add preserve_order feature to use LinkedHashMap instead of BTreeMap chyh1990/yaml-rust#16
• Preserve order of map keys dtolnay/serde-yaml#14 Preserve order of map keys dtolnay/serde-yaml#14

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#269 (comment)

[dtolnay]

All set here, I think. The answer is to use an ordered map type (linked-hash-map and linear-map both come with serde support). For YAML you additionally need to set the preserve_order feature flag to force yaml-rust to use LinkedHashMap instead of BTreeMap. This issue can be closed.

[oli-obk]

Should we add this feature to the json value type?

[calebmer]

Awesome, thanks! @oli-obk, maybe that should be a fresh issue?

[dtolnay]

I filed serde-rs/json#54 to follow up on adding a feature flag to use linked-hash-map in serde_json::Value.