Struct Value

pub struct Value(/* private fields */);

Generic value type for data passed through header.

Implementations

impl Value

pub fn new(value: impl Into<Value>) -> Self

Creates a new Value by converting value to the underlying type.

pub fn to_vec(&self) -> Result<Vec<u8>>

Serializes the value into bytes.

pub fn from_slice(slice: &[u8]) -> Result<Self>

Deserializes the value from bytes.

pub fn cast_as<T>(self) -> Result<T>

where T: DeserializeOwned,

Attempts to convert this generic value to a specific type.

Methods from Deref<Target = Value>

pub fn get<I>(&self, index: I) -> Option<&Value>

where I: Index,

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));

pub fn get_mut<I>(&mut self, index: I) -> Option<&mut Value>

where I: Index,

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");

pub fn is_object(&self) -> bool

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());

pub fn as_object(&self) -> Option<&Map<String, Value>>

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);

pub fn as_object_mut(&mut self) -> Option<&mut Map<String, Value>>

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": {} }));

pub fn is_array(&self) -> bool

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());

pub fn as_array(&self) -> Option<&Vec<Value>>

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);

pub fn as_array_mut(&mut self) -> Option<&mut Vec<Value>>

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": [] }));

pub fn is_string(&self) -> bool

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());

pub fn as_str(&self) -> Option<&str>

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());

pub fn is_number(&self) -> bool

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());

pub fn as_number(&self) -> Option<&Number>

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

let v = json!({ "a": 1, "b": 2.2, "c": -3, "d": "4" });

assert_eq!(v["a"].as_number(), Some(&Number::from(1u64)));
assert_eq!(v["b"].as_number(), Some(&Number::from_f64(2.2).unwrap()));
assert_eq!(v["c"].as_number(), Some(&Number::from(-3i64)));

// The string `"4"` is not a number.
assert_eq!(v["d"].as_number(), None);

pub fn is_i64(&self) -> bool

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());

pub fn is_u64(&self) -> bool

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());

pub fn is_f64(&self) -> bool

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());

pub fn as_i64(&self) -> Option<i64>

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);

pub fn as_u64(&self) -> Option<u64>

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);

pub fn as_f64(&self) -> Option<f64>

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));

pub fn is_boolean(&self) -> bool

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());

pub fn as_bool(&self) -> Option<bool>

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);

pub fn is_null(&self) -> bool

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());

pub fn as_null(&self) -> Option<()>

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);

pub fn pointer(&self, pointer: &str) -> Option<&Value>

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);

pub fn pointer_mut(&mut self, pointer: &str) -> Option<&mut Value>

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);
}

pub fn take(&mut self) -> Value

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 }));

pub fn sort_all_objects(&mut self)

Reorders the entries of all Value::Object nested within this JSON value according to str’s usual ordering.

If serde_json’s “preserve_order” feature is not enabled, this method does no work because all JSON maps are always kept in a sorted state.

If serde_json’s “preserve_order” feature is enabled, this method destroys the original source order or insertion order of the JSON objects in favor of an alphanumerical order that matches how a BTreeMap with the same contents would be ordered.

Trait Implementations

impl Clone for Value

fn clone(&self) -> Value

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Value

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Deref for Value

type Target = Value

The resulting type after dereferencing.

fn deref(&self) -> &Self::Target

Dereferences the value.

impl DerefMut for Value

fn deref_mut(&mut self) -> &mut Self::Target

Mutably dereferences the value.

impl<'de> Deserialize<'de> for Value

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl<'a, T> From<&'a [T]> for Value

where T: Clone + Into<Value>,

fn from(x: &'a [T]) -> Self

Converts to this type from the input type.

impl<'a> From<&'a str> for Value

fn from(x: &'a str) -> Self

Converts to this type from the input type.

impl From<()> for Value

fn from(x: ()) -> Self

Converts to this type from the input type.

impl<'a> From<Cow<'a, str>> for Value

fn from(x: Cow<'a, str>) -> Self

Converts to this type from the input type.

impl From<Map<String, Value>> for Value

fn from(x: Map<String, Value>) -> Self

Converts to this type from the input type.

impl From<Number> for Value

fn from(x: Number) -> Self

Converts to this type from the input type.

impl<T> From<Option<T>> for Value

where T: Into<Value>,

fn from(x: Option<T>) -> Self

Converts to this type from the input type.

impl From<String> for Value

fn from(x: String) -> Self

Converts to this type from the input type.

impl<T> From<Vec<T>> for Value

where T: Into<Value>,

fn from(x: Vec<T>) -> Self

Converts to this type from the input type.

impl From<bool> for Value

fn from(x: bool) -> Self

Converts to this type from the input type.

impl From<f32> for Value

fn from(x: f32) -> Self

Converts to this type from the input type.

impl From<f64> for Value

fn from(x: f64) -> Self

Converts to this type from the input type.

impl From<i16> for Value

fn from(x: i16) -> Self

Converts to this type from the input type.

impl From<i32> for Value

fn from(x: i32) -> Self

Converts to this type from the input type.

impl From<i64> for Value

fn from(x: i64) -> Self

Converts to this type from the input type.

impl From<i8> for Value

fn from(x: i8) -> Self

Converts to this type from the input type.

impl From<isize> for Value

fn from(x: isize) -> Self

Converts to this type from the input type.

impl From<u16> for Value

fn from(x: u16) -> Self

Converts to this type from the input type.

impl From<u32> for Value

fn from(x: u32) -> Self

Converts to this type from the input type.

impl From<u64> for Value

fn from(x: u64) -> Self

Converts to this type from the input type.

impl From<u8> for Value

fn from(x: u8) -> Self

Converts to this type from the input type.

impl From<usize> for Value

fn from(x: usize) -> Self

Converts to this type from the input type.

impl PartialEq for Value

fn eq(&self, other: &Value) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Serialize for Value

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl Eq for Value

impl StructuralPartialEq for Value