Enum serde_json :: value :: Value

Index into a JSON array or map. A string index can be used to access a value in a map, and a usize index can be used to access an element of an array.

Returns None if the type of self does not match the type of the index, for example if the index is a string and self is an array or a number. Also returns None if the given key does not exist in the map or the given index is not within the bounds of the array.

let object = json!({ "A": 65, "B": 66, "C": 67 });
assert_eq!(*object.get("A").unwrap(), json!(65));
let array = json!([ "A", "B", "C" ]);
assert_eq!(*array.get(2).unwrap(), json!("C"));
assert_eq!(array.get("A"), None);

Square brackets can also be used to index into a value in a more concise way. This returns Value::Null in cases where get would have returned None .

let object = json!({
    "A": ["a", "á", "à"],
    "B": ["b", "b́"],
    "C": ["c", "ć", "ć̣", "ḉ"],
assert_eq!(object["B"][0], json!("b"));
assert_eq!(object["D"], json!(null));
assert_eq!(object[0]["x"]["y"]["z"], json!(null));

Mutably index into a JSON array or map. A string index can be used to access a value in a map, and a usize index can be used to access an element of an array.

Returns None if the type of self does not match the type of the index, for example if the index is a string and self is an array or a number. Also returns None if the given key does not exist in the map or the given index is not within the bounds of the array.

let mut object = json!({ "A": 65, "B": 66, "C": 67 });
*object.get_mut("A").unwrap() = json!(69);
let mut array = json!([ "A", "B", "C" ]);
*array.get_mut(2).unwrap() = json!("D");

Returns true if the Value is an Object. Returns false otherwise.

For any Value on which is_object returns true, as_object and as_object_mut are guaranteed to return the map representation of the object.

let obj = json!({ "a": { "nested": true }, "b": ["an", "array"] });
assert!(obj.is_object());
assert!(obj["a"].is_object());
// array, not an object
assert!(!obj["b"].is_object());

If the Value is an Object, returns the associated Map. Returns None otherwise.

let v = json!({ "a": { "nested": true }, "b": ["an", "array"] });
// The length of `{"nested": true}` is 1 entry.
assert_eq!(v["a"].as_object().unwrap().len(), 1);
// The array `["an", "array"]` is not an object.
assert_eq!(v["b"].as_object(), None);

If the Value is an Object, returns the associated mutable Map. Returns None otherwise.

let mut v = json!({ "a": { "nested": true } });
v["a"].as_object_mut().unwrap().clear();
assert_eq!(v, json!({ "a": {} }));

Returns true if the Value is an Array. Returns false otherwise.

For any Value on which is_array returns true, as_array and as_array_mut are guaranteed to return the vector representing the array.

let obj = json!({ "a": ["an", "array"], "b": { "an": "object" } });
assert!(obj["a"].is_array());
// an object, not an array
assert!(!obj["b"].is_array());

If the Value is an Array, returns the associated vector. Returns None otherwise.

let v = json!({ "a": ["an", "array"], "b": { "an": "object" } });
// The length of `["an", "array"]` is 2 elements.
assert_eq!(v["a"].as_array().unwrap().len(), 2);
// The object `{"an": "object"}` is not an array.
assert_eq!(v["b"].as_array(), None);

If the Value is an Array, returns the associated mutable vector. Returns None otherwise.

let mut v = json!({ "a": ["an", "array"] });
v["a"].as_array_mut().unwrap().clear();
assert_eq!(v, json!({ "a": [] }));

Returns true if the Value is a String. Returns false otherwise.

For any Value on which is_string returns true, as_str is guaranteed to return the string slice.

let v = json!({ "a": "some string", "b": false });
assert!(v["a"].is_string());
// The boolean `false` is not a string.
assert!(!v["b"].is_string());

If the Value is a String, returns the associated str. Returns None otherwise.

let v = json!({ "a": "some string", "b": false });
assert_eq!(v["a"].as_str(), Some("some string"));
// The boolean `false` is not a string.
assert_eq!(v["b"].as_str(), None);
// JSON values are printed in JSON representation, so strings are in quotes.
//    The value is: "some string"
println!("The value is: {}", v["a"]);
// Rust strings are printed without quotes.
//    The value is: some string
println!("The value is: {}", v["a"].as_str().unwrap());

Returns true if the Value is a Number. Returns false otherwise.

let v = json!({ "a": 1, "b": "2" });
assert!(v["a"].is_number());
// The string `"2"` is a string, not a number.
assert!(!v["b"].is_number());

Returns true if the Value is an integer between i64::MIN and i64::MAX .

For any Value on which is_i64 returns true, as_i64 is guaranteed to return the integer value.

let big = i64::max_value() as u64 + 10;
let v = json!({ "a": 64, "b": big, "c": 256.0 });
assert!(v["a"].is_i64());
// Greater than i64::MAX.
assert!(!v["b"].is_i64());
// Numbers with a decimal point are not considered integers.
assert!(!v["c"].is_i64());

Returns true if the Value is an integer between zero and u64::MAX .

For any Value on which is_u64 returns true, as_u64 is guaranteed to return the integer value.

let v = json!({ "a": 64, "b": -64, "c": 256.0 });
assert!(v["a"].is_u64());
// Negative integer.
assert!(!v["b"].is_u64());
// Numbers with a decimal point are not considered integers.
assert!(!v["c"].is_u64());

Returns true if the Value is a number that can be represented by f64.

For any Value on which is_f64 returns true, as_f64 is guaranteed to return the floating point value.

Currently this function returns true if and only if both is_i64 and is_u64 return false but this is not a guarantee in the future.

let v = json!({ "a": 256.0, "b": 64, "c": -64 });
assert!(v["a"].is_f64());
// Integers.
assert!(!v["b"].is_f64());
assert!(!v["c"].is_f64());

If the Value is an integer, represent it as i64 if possible. Returns None otherwise.

let big = i64::max_value() as u64 + 10;
let v = json!({ "a": 64, "b": big, "c": 256.0 });
assert_eq!(v["a"].as_i64(), Some(64));
assert_eq!(v["b"].as_i64(), None);
assert_eq!(v["c"].as_i64(), None);

If the Value is an integer, represent it as u64 if possible. Returns None otherwise.

let v = json!({ "a": 64, "b": -64, "c": 256.0 });
assert_eq!(v["a"].as_u64(), Some(64));
assert_eq!(v["b"].as_u64(), None);
assert_eq!(v["c"].as_u64(), None);

If the Value is a number, represent it as f64 if possible. Returns None otherwise.

let v = json!({ "a": 256.0, "b": 64, "c": -64 });
assert_eq!(v["a"].as_f64(), Some(256.0));
assert_eq!(v["b"].as_f64(), Some(64.0));
assert_eq!(v["c"].as_f64(), Some(-64.0));

Returns true if the Value is a Boolean. Returns false otherwise.

For any Value on which is_boolean returns true, as_bool is guaranteed to return the boolean value.

let v = json!({ "a": false, "b": "false" });
assert!(v["a"].is_boolean());
// The string `"false"` is a string, not a boolean.
assert!(!v["b"].is_boolean());

If the Value is a Boolean, returns the associated bool. Returns None otherwise.

let v = json!({ "a": false, "b": "false" });
assert_eq!(v["a"].as_bool(), Some(false));
// The string `"false"` is a string, not a boolean.
assert_eq!(v["b"].as_bool(), None);

Returns true if the Value is a Null. Returns false otherwise.

For any Value on which is_null returns true, as_null is guaranteed to return Some(()) .

let v = json!({ "a": null, "b": false });
assert!(v["a"].is_null());
// The boolean `false` is not null.
assert!(!v["b"].is_null());

If the Value is a Null, returns (). Returns None otherwise.

let v = json!({ "a": null, "b": false });
assert_eq!(v["a"].as_null(), Some(()));
// The boolean `false` is not null.
assert_eq!(v["b"].as_null(), None);

Looks up a value by a JSON Pointer.

JSON Pointer defines a string syntax for identifying a specific value within a JavaScript Object Notation (JSON) document.

A Pointer is a Unicode string with the reference tokens separated by / . Inside tokens / is replaced by ~1 and ~ is replaced by ~0 . The addressed value is returned and if there is no such value None is returned.

For more information read RFC6901 .

Examples

let data = json!({
    "x": {
        "y": ["z", "zz"]
assert_eq!(data.pointer("/x/y/1").unwrap(), &json!("zz"));
assert_eq!(data.pointer("/a/b/c"), None);

Looks up a value by a JSON Pointer and returns a mutable reference to that value.

JSON Pointer defines a string syntax for identifying a specific value within a JavaScript Object Notation (JSON) document.

A Pointer is a Unicode string with the reference tokens separated by / . Inside tokens / is replaced by ~1 and ~ is replaced by ~0 . The addressed value is returned and if there is no such value None is returned.

For more information read RFC6901 .

Example of Use

use serde_json::Value;
fn main() {
    let s = r#"{"x": 1.0, "y": 2.0}"#;
    let mut value: Value = serde_json::from_str(s).unwrap();
    // Check value using read-only pointer
    assert_eq!(value.pointer("/x"), Some(&1.0.into()));
    // Change value with direct assignment
    *value.pointer_mut("/x").unwrap() = 1.5.into();
    // Check that new value was written
    assert_eq!(value.pointer("/x"), Some(&1.5.into()));
    // Or change the value only if it exists
    value.pointer_mut("/x").map(|v| *v = 1.5.into());
    // "Steal" ownership of a value. Can replace with any valid Value.
    let old_x = value.pointer_mut("/x").map(Value::take).unwrap();
    assert_eq!(old_x, 1.5




    
);
    assert_eq!(value.pointer("/x").unwrap(), &Value::Null);

Takes the value out of the Value , leaving a Null in its place.

let mut v = json!({ "x": "y" });
assert_eq!(v["x"].take(), json!("y"));
assert_eq!(v, json!({ "x": null }));

Display a JSON value as a string.

let json = json!({ "city": "London", "street": "10 Downing Street" });
// Compact format:
// {"city":"London","street":"10 Downing Street"}
let compact = format!("{}", json);
assert_eq!




    
(compact,
    "{\"city\":\"London\",\"street\":\"10 Downing Street\"}");
// Pretty format:
//   "city": "London",
//   "street": "10 Downing Street"
let pretty = format!("{:#}", json);
assert_eq!(pretty,
    "{\n  \"city\": \"London\",\n  \"street\": \"10 Downing Street\"\n}");

Convert a slice to Value

use serde_json::Value;
let v: &[&str] = &["lorem", "ipsum", "dolor"];
let x: Value = v.into();

Convert string slice to Value

use serde_json::Value;
let s: &str = "lorem";
let x: Value = s.into();

Convert () to Value

use serde_json::Value;
let u = ();
let x: Value = u.into();

Convert copy-on-write string to Value

use serde_json::Value;
use std::borrow::Cow;
let s: Cow<str> = Cow::Borrowed("lorem");
let x: Value = s.into();

use serde_json::Value;
use std::borrow::Cow;
let s: Cow<str> = Cow::Owned("lorem".to_string());
let x: Value = s.into();

Convert map (with string keys) to Value

use serde_json::{Map, Value};
let mut m = Map::new();
m.insert("Lorem".to_string(), "ipsum".into());
let x: Value = m.into();

Convert Number to Value

use serde_json::{Number, Value};
let n = Number::from(7);
let x: Value = n.into();

Convert String to Value

use serde_json::Value;
let s: String = "lorem".to_string();
let x: Value = s.into();

Convert a Vec to Value

use serde_json::Value;
let v = vec!["lorem", "ipsum", "dolor"];
let x: Value = v.into();

Convert boolean to Value

use serde_json::Value;
let b = false;
let x: Value = b.into();

Convert 32-bit floating point number to Value

use serde_json::Value;
let f: f32 = 13.37;
let x: Value = f.into();

Convert 64-bit floating point number to Value

use serde_json::Value;
let f: f64 = 13.37;
let x: Value = f.into();

Convert an iteratable type to a Value

use serde_json::Value;
let v: Vec<_> = vec![("lorem", 40), ("ipsum", 2)];
let x: Value = v.into_iter().collect();

Convert an iteratable type to a Value

use serde_json::Value;
let v = std::iter::repeat(42).take(5);
let x: Value = v.collect();

use serde_json::Value;
let v: Vec<_> = vec!["lorem", "ipsum", "dolor"];
let x: Value = v.into_iter().collect();

use std::iter::FromIterator;
use serde_json::Value;
let x: Value = Value::from_iter(vec!["lorem", "ipsum", "dolor"]);

Index into a serde_json::Value using the syntax value[0] or value["k"] .

let data = json!({
    "x": {
        "y": ["z", "zz"]
assert_eq!(data["x"]["y"], json!(["z", "zz"]));
assert_eq!(data["x"]["y"][0], json!("z"));
assert_eq!(data["a"], json!(null)); // returns null for undefined values
assert_eq!(data["a"]["b"], json!(null)); // does not panic

Write into a serde_json::Value using the syntax value[0] = ... or value["k"] = ... .

let mut data = json!({ "x": 0 });
// replace an existing key
data["x"] = json!(1);
// insert a new key
data["y"] = json!([false, false, false]);
// replace an array value
data["y"][0] = json!(true);
// inserted a deeply nested key
data["a"]["b"]["c"]["d"] = json!(true);
println!("{}", data);

Returns the argument unchanged.

Calls U::from(self) .