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0.0.9 Jun 20, 2022
0.0.8 May 22, 2022
0.0.5 Nov 17, 2021

#169 in Encoding

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1,098 downloads per month
Used in 6 crates (via progenitor-impl)


6.5K SLoC


Compile JSON Schema documents into Rust types. This can be used ...

  • via the macro import_types!("types.json") to generate Rust types directly in your program

  • via a builder interface to generate Rust types in build.rs

  • or via the builder functions to generate persistent files e.g. when building API bindings.

JSON Schema → Rust types

We can divide types in JSON Schema into a few classes:

Simple types

Integers, floating-point numbers, strings, etc. Those all have straightforward translations. The only significant nuance is how to select the appropriate built-in type.


JSON Schema arrays can turn into three Rust types Vec<T>, HashSet<T>, and tuples. Arrays may have a fixed length that matches a fixed list of item types; this matches well with Rust tuples. The distintion between Vec<T> and HashSet<T> is only if the uniqueItems field is true.


In general Objects turn in to Rust structs, but if there are no properties defined Typify models this as a HashMap<String, T> if the additionalProperties schema specifies T or a HashMap<String, serde_json::Value> otherwise. Properties that are not in the required set and represented as an Option<T>.


The OneOf construct maps to a Rust enum. Typify maps this to the various serde enum types.

AnyOf / AllOf

The anyOf and allOf constructs are a little trickier to handle, but (in general) Typify models these as structs where each member is decorated with the #[serde(flatten)] attribute.


Typify is a work in progress. Changes that affect output will likely be breaking changes. We will continue to update the crate version number with each change; be cognizant when updating to a new version.

Bounded numbers aren't very well handled. Consider, for example, the schema:

    "type": "integer",
    "minimum": 1,
    "maximum": 6

The resulting types won't enforce those value constraints.

Similarly, patterns and lengths for strings are not enforced.

In general, if you have a JSON Schema that causes Typify to fail or if the generated type isn't what you expect, please file an issue.


~101K SLoC