Crate jzon 

jzon — purpose-built, zero-copy JSON serialization for specific structs.

Design

Use #[derive(ToJson, FromJson)] to generate a monomorphised JSON (de)serializer for each of your types at compile time. No generic visitor indirection, no intermediate Value allocation, no format-string overhead.

Cargo features

Feature	Default	Effect
derive	✓	#[derive(ToJson, FromJson)] proc-macros
simd		u128 SWAR scanning (16 B/iter)
simd + unstable		std::simd portable SIMD (32–64 B/iter, nightly)
fast-float		ryu serialization, fast_float2 parsing
stats		ScannerStats allocation/cache-hit counters

For serde integration see jzon-rs-serde. For a serde_json drop-in see jzon-rs-compat.

Zero-copy deserialization

Fields typed &'de str borrow directly from the input — no String is allocated unless the JSON string contains escape sequences.

Field-hint cache

The generated FromJson impl maintains a one-word field-hint variable that predicts which field key to expect next. For JSON whose field order matches the struct definition — the common case — almost every key dispatch is O(1) without hashing.

Safe Rust only

There are no unsafe blocks in this crate. All SIMD scanning uses std::simd (nightly) or pure u64/u128 arithmetic (SWAR).

Quick start

use jzon::{ToJson, FromJson};

#[derive(ToJson, FromJson, Debug, PartialEq)]
#[serde(rename_all = "camelCase")]
struct User<'a> {
    user_id:  u64,
    name:     &'a str,
    #[serde(skip_serializing_if = "Option::is_none")]
    email:    Option<String>,
    #[serde(default)]
    score:    f64,
}

let input = r#"{"userId":1,"name":"alice","score":9.5}"#;
let user: User = User::from_json_str(input).unwrap();
let out = user.to_json_string();

Re-exports

pub use error::Error;

pub use scanner::JsonStr;

pub use scanner::Scanner;

pub use ser::ToJson;

pub use de::FromJson;

pub use fixed::FixedBuf;

pub use fixed::ToJsonExt;

pub use fixed::json_str_len;

Modules

de

FromJson<'de> trait and primitive implementations.

error

fixed

Zero-allocation, stack-based JSON output via const-generic fixed buffers.

scanner

ser

ToJson trait and primitive implementations.

simd

Derive Macros

FromJson

Derive jzon::FromJson<'de> for a named struct or unit/tuple-less enum.

ToJson

Derive jzon::ToJson for a named struct or unit/tuple-less enum.