std.json

Parse, build, and stringify JSON. The module provides a single Json value type that represents all JSON forms.

import std.json

Errors

pub error JsonError {
    message: string
}

json.parse() raises JsonError on invalid input.

Constructors

Build JSON values programmatically:

json.null() Json
json.bool(v: bool) Json
json.int(v: int) Json
json.float(v: float) Json
json.string(v: string) Json
json.array() Json
json.object() Json

let obj = json.object()
obj.set("name", json.string("Alice"))
obj.set("age", json.int(30))
obj.set("active", json.bool(true))

let items = json.array()
items.push(json.int(1))
items.push(json.int(2))
obj.set("scores", items)

Parsing

json.parse(s: string) Json     // raises JsonError

let data = json.parse("{\"name\": \"Alice\", \"age\": 30}")!
let name = data.get("name").get_string()
let age = data.get("age").get_int()

Json Methods

Type Checks

j.is_null() bool
j.is_bool() bool
j.is_int() bool
j.is_float() bool
j.is_string() bool
j.is_array() bool
j.is_object() bool

Value Extraction

j.get_bool() bool
j.get_int() int
j.get_float() float
j.get_string() string

get_int() on a float value truncates. get_float() on an int value converts.

Traversal

j.get(key: string) Json     // object field lookup; returns json.null() if missing
j.at(index: int) Json       // array index access
j.len() int                 // array or object length

Mutation

j.set(key: string, value: Json)    // set or overwrite an object field
j.push(value: Json)                // append to an array

Serialization

j.to_string() string    // JSON-encoded string

Example: Round-Trip

import std.json

fn main() {
    let mut response = json.object()
    response.set("status", json.string("ok"))
    response.set("count", json.int(3))

    let mut items = json.array()
    items.push(json.string("apple"))
    items.push(json.string("banana"))
    response.set("items", items)

    let s = response.to_string()
    print(s)
    // {"status":"ok","count":3,"items":["apple","banana"]}

    let parsed = json.parse(s)!
    print(parsed.get("status").get_string())    // ok
    print(f"{parsed.get("count").get_int()!}")    // 3
}