JSON (serde/json)

The JSON module is the most heavily used format in serde. It provides a complete encoder, decoder, and a tree-based JsonValue type for dynamic data access.

Modules

File	Purpose
encoder.vx	Struct → JSON string serialization
decoder.vx	JSON string → Struct deserialization
value.vx	JsonValue dynamic tree (Object, Array, String, Number, Bool, Null)
serde.vx	Contract-based Serializer/Deserializer implementations

Encoding (Struct → JSON)

import { encode } from "serde/json";

struct User {
    id: i64
    name: string
    active: bool
}

let user = User { id: 1, name: "Alice", active: true };
let json = encode<User>(&user);
// → {"id":1,"name":"Alice","active":true}

The encoder walks struct fields at compile-time offsets, emitting keys and values directly into a growable buffer. No reflection, no hash maps—just raw byte writes.

Decoding (JSON → Struct)

import { decode } from "serde/json";

let payload = "{\"id\":42,\"name\":\"Bob\",\"active\":false}";
let! user = User { };
decode<User>(payload, &user);
println("Name: {user.name}");  // Name: Bob

The decoder uses a streaming byte scanner to walk the JSON token stream. When it encounters a key, it uses seekToKey to match against known struct field names and directly writes the parsed value into the struct's memory layout.

Dynamic JSON (JsonValue)

For untyped or heterogeneous JSON, use JsonValue:

import { parseJSON } from "serde/json";

let val = parseJSON("{\"users\":[{\"name\":\"Alice\"},{\"name\":\"Bob\"}]}");
// Access nested values via the JsonValue tree

String Escaping

The encoder handles all JSON string escaping requirements (backslash, quotes, control characters, Unicode escapes) automatically during serialization.