//! The Value enum, a loosely typed way of representing any valid JSON value.
//!
//! # Constructing JSON
//!
//! Serde JSON provides a [`json!` macro][macro] to build `serde_json::Value`
//! objects with very natural JSON syntax.
//!
//! ```
//! use serde_json::json;
//!
//! fn main() {
//! // The type of `john` is `serde_json::Value`
//! let john = json!({
//! "name": "John Doe",
//! "age": 43,
//! "phones": [
//! "+44 1234567",
//! "+44 2345678"
//! ]
//! });
//!
//! println!("first phone number: {}", john["phones"][0]);
//!
//! // Convert to a string of JSON and print it out
//! println!("{}", john.to_string());
//! }
//! ```
//!
//! The `Value::to_string()` function converts a `serde_json::Value` into a
//! `String` of JSON text.
//!
//! One neat thing about the `json!` macro is that variables and expressions can
//! be interpolated directly into the JSON value as you are building it. Serde
//! will check at compile time that the value you are interpolating is able to
//! be represented as JSON.
//!
//! ```
//! # use serde_json::json;
//! #
//! # fn random_phone() -> u16 { 0 }
//! #
//! let full_name = "John Doe";
//! let age_last_year = 42;
//!
//! // The type of `john` is `serde_json::Value`
//! let john = json!({
//! "name": full_name,
//! "age": age_last_year + 1,
//! "phones": [
//! format!("+44 {}", random_phone())
//! ]
//! });
//! ```
//!
//! A string of JSON data can be parsed into a `serde_json::Value` by the
//! [`serde_json::from_str`][from_str] function. There is also
//! [`from_slice`][from_slice] for parsing from a byte slice `&[u8]` and
//! [`from_reader`][from_reader] for parsing from any `io::Read` like a File or
//! a TCP stream.
//!
//! ```
//! use serde_json::{json, Value, Error};
//!
//! fn untyped_example() -> Result<(), Error> {
//! // Some JSON input data as a &str. Maybe this comes from the user.
//! let data = r#"
//! {
//! "name": "John Doe",
//! "age": 43,
//! "phones": [
//! "+44 1234567",
//! "+44 2345678"
//! ]
//! }"#;
//!
//! // Parse the string of data into serde_json::Value.
//! let v: Value = serde_json::from_str(data)?;
//!
//! // Access parts of the data by indexing with square brackets.
//! println!("Please call {} at the number {}", v["name"], v["phones"][0]);
//!
//! Ok(())
//! }
//! #
//! # untyped_example().unwrap();
//! ```
//!
//! [macro]: crate::json
//! [from_str]: crate::de::from_str
//! [from_slice]: crate::de::from_slice
//! [from_reader]: crate::de::from_reader
use crate::error::Error;
use crate::io;
use alloc::string::String;
use alloc::vec::Vec;
use core::fmt::{self, Debug, Display};
use core::mem;
use core::str;
use serde::de::DeserializeOwned;
use serde::ser::Serialize;
pub use self::index::Index;
pub use self::ser::Serializer;
pub use crate::map::Map;
pub use crate::number::Number;
#[cfg(feature = "raw_value")]
#[cfg_attr(docsrs, doc(cfg(feature = "raw_value")))]
pub use crate::raw::{to_raw_value, RawValue};
/// Represents any valid JSON value.
///
/// See the [`serde_json::value` module documentation](self) for usage examples.
#[derive(Clone, Eq, PartialEq)]
pub enum Value {
/// Represents a JSON null value.
///
/// ```
/// # use serde_json::json;
/// #
/// let v = json!(null);
/// ```
Null,
/// Represents a JSON boolean.
///
/// ```
/// # use serde_json::json;
/// #
/// let v = json!(true);
/// ```
Bool(bool),
/// Represents a JSON number, whether integer or floating point.
///
/// ```
/// # use serde_json::json;
/// #
/// let v = json!(12.5);
/// ```
Number(Number),
/// Represents a JSON string.
///
/// ```
/// # use serde_json::json;
/// #
/// let v = json!("a string");
/// ```
String(String),
/// Represents a JSON array.
///
/// ```
/// # use serde_json::json;
/// #
/// let v = json!(["an", "array"]);
/// ```
Array(Vec<Value>),
/// Represents a JSON object.
///
/// By default the map is backed by a BTreeMap. Enable the `preserve_order`
/// feature of serde_json to use IndexMap instead, which preserves
/// entries in the order they are inserted into the map. In particular, this
/// allows JSON data to be deserialized into a Value and serialized to a
/// string while retaining the order of map keys in the input.
///
/// ```
/// # use serde_json::json;
/// #
/// let v = json!({ "an": "object" });
/// ```
Object(Map<String, Value>),
}
impl Debug for Value {
fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
match self {
Value::Null => formatter.write_str("Null"),
Value::Bool(boolean) => write!(formatter, "Bool({})", boolean),
Value::Number(number) => Debug::fmt(number, formatter),
Value::String(string) => write!(formatter, "String({:?})", string),
Value::Array(vec) => {
tri!(formatter.write_str("Array "));
Debug::fmt(vec, formatter)
}
Value::Object(map) => {
tri!(formatter.write_str("Object "));
Debug::fmt(map, formatter)
}
}
}
}
impl Display for Value {
/// Display a JSON value as a string.
///
/// ```
/// # use serde_json::json;
/// #
/// 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}");
/// ```
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
struct WriterFormatter<'a, 'b: 'a> {
inner: &'a mut fmt::Formatter<'b>,
}
impl<'a, 'b> io::Write for WriterFormatter<'a, 'b> {
fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
// Safety: the serializer below only emits valid utf8 when using
// the default formatter.
let s = unsafe { str::from_utf8_unchecked(buf) };
tri!(self.inner.write_str(s).map_err(io_error));
Ok(buf.len())
}
fn flush(&mut self) -> io::Result<()> {
Ok(())
}
}
fn io_error(_: fmt::Error) -> io::Error {
// Error value does not matter because Display impl just maps it
// back to fmt::Error.
io::Error::new(io::ErrorKind::Other, "fmt error")
}
let alternate = f.alternate();
let mut wr = WriterFormatter { inner: f };
if alternate {
// {:#}
super::ser::to_writer_pretty(&mut wr, self).map_err(|_| fmt::Error)
} else {
// {}
super::ser::to_writer(&mut wr, self).map_err(|_| fmt::Error)
}
}
}
fn parse_index(s: &str) -> Option<usize> {
if s.starts_with('+') || (s.starts_with('0') && s.len() != 1) {
return None;
}
s.parse().ok()
}
impl 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.
///
/// ```
/// # use serde_json::json;
/// #
/// 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`.
///
/// ```
/// # use serde_json::json;
/// #
/// 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<I: Index>(&self, index: I) -> Option<&Value> {
index.index_into(self)
}
/// 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.
///
/// ```
/// # use serde_json::json;
/// #
/// 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 get_mut<I: Index>(&mut self, index: I) -> Option<&mut Value> {
index.index_into_mut(self)
}
/// 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.
///
/// ```
/// # use serde_json::json;
/// #
/// 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 is_object(&self) -> bool {
self.as_object().is_some()
}
/// If the `Value` is an Object, returns the associated Map. Returns None
/// otherwise.
///
/// ```
/// # use serde_json::json;
/// #
/// 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(&self) -> Option<&Map<String, Value>> {
match self {
Value::Object(map) => Some(map),
_ => None,
}
}
/// If the `Value` is an Object, returns the associated mutable Map.
/// Returns None otherwise.
///
/// ```
/// # use serde_json::json;
/// #
/// let mut v = json!({ "a": { "nested": true } });
///
/// v["a"].as_object_mut().unwrap().clear();
/// assert_eq!(v, json!({ "a": {} }));
/// ```
pub fn as_object_mut(&mut self) -> Option<&mut Map<String, Value>> {
match self {
Value::Object(map) => Some(map),
_ => None,
}
}
/// 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.
///
/// ```
/// # use serde_json::json;
/// #
/// 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 is_array(&self) -> bool {
self.as_array().is_some()
}
/// If the `Value` is an Array, returns the associated vector. Returns None
/// otherwise.
///
/// ```
/// # use serde_json::json;
/// #
/// 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(&self) -> Option<&Vec<Value>> {
match self {
Value::Array(array) => Some(array),
_ => None,
}
}
/// If the `Value` is an Array, returns the associated mutable vector.
/// Returns None otherwise.
///
/// ```
/// # use serde_json::json;
/// #
/// let mut v = json!({ "a": ["an", "array"] });
///
/// v["a"].as_array_mut().unwrap().clear();
/// assert_eq!(v, json!({ "a": [] }));
/// ```
pub fn as_array_mut(&mut self) -> Option<&mut Vec<Value>> {
match self {
Value::Array(list) => Some(list),
_ => None,
}
}
/// 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.
///
/// ```
/// # use serde_json::json;
/// #
/// 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 is_string(&self) -> bool {
self.as_str().is_some()
}
/// If the `Value` is a String, returns the associated str. Returns None
/// otherwise.
///
/// ```
/// # use serde_json::json;
/// #
/// 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 as_str(&self) -> Option<&str> {
match self {
Value::String(s) => Some(s),
_ => None,
}
}
/// Returns true if the `Value` is a Number. Returns false otherwise.
///
/// ```
/// # use serde_json::json;
/// #
/// 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 is_number(&self) -> bool {
match *self {
Value::Number(_) => true,
_ => false,
}
}
/// If the `Value` is a Number, returns the associated [`Number`]. Returns
/// None otherwise.
///
/// ```
/// # use serde_json::{json, Number};
/// #
/// 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 as_number(&self) -> Option<&Number> {
match self {
Value::Number(number) => Some(number),
_ => None,
}
}
/// 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.
///
/// ```
/// # use serde_json::json;
/// #
/// 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_i64(&self) -> bool {
match self {
Value::Number(n) => n.is_i64(),
_ => false,
}
}
/// 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.
///
/// ```
/// # use serde_json::json;
/// #
/// 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_u64(&self) -> bool {
match self {
Value::Number(n) => n.is_u64(),
_ => false,
}
}
/// 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.
///
/// ```
/// # use serde_json::json;
/// #
/// 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 is_f64(&self) -> bool {
match self {
Value::Number(n) => n.is_f64(),
_ => false,
}
}
/// If the `Value` is an integer, represent it as i64 if possible. Returns
/// None otherwise.
///
/// ```
/// # use serde_json::json;
/// #
/// 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_i64(&self) -> Option<i64> {
match self {
Value::Number(n) => n.as_i64(),
_ => None,
}
}
/// If the `Value` is an integer, represent it as u64 if possible. Returns
/// None otherwise.
///
/// ```
/// # use serde_json::json;
/// #
/// 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_u64(&self) -> Option<u64> {
match self {
Value::Number(n) => n.as_u64(),
_ => None,
}
}
/// If the `Value` is a number, represent it as f64 if possible. Returns
/// None otherwise.
///
/// ```
/// # use serde_json::json;
/// #
/// 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 as_f64(&self) -> Option<f64> {
match self {
Value::Number(n) => n.as_f64(),
_ => None,
}
}
/// 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.
///
/// ```
/// # use serde_json::json;
/// #
/// 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 is_boolean(&self) -> bool {
self.as_bool().is_some()
}
/// If the `Value` is a Boolean, returns the associated bool. Returns None
/// otherwise.
///
/// ```
/// # use serde_json::json;
/// #
/// 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 as_bool(&self) -> Option<bool> {
match *self {
Value::Bool(b) => Some(b),
_ => 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(())`.
///
/// ```
/// # use serde_json::json;
/// #
/// 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 is_null(&self) -> bool {
self.as_null().is_some()
}
/// If the `Value` is a Null, returns (). Returns None otherwise.
///
/// ```
/// # use serde_json::json;
/// #
/// 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 as_null(&self) -> Option<()> {
match *self {
Value::Null => Some(()),
_ => 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](
https://tools.ietf.org/html/rfc6901).
///
/// # Examples
///
/// ```
/// # use serde_json::json;
/// #
/// 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(&self, pointer: &str) -> Option<&Value> {
if pointer.is_empty() {
return Some(self);
}
if !pointer.starts_with('/') {
return None;
}
pointer
.split('/')
.skip(1)
.map(|x| x.replace("~1", "/").replace("~0", "~"))
.try_fold(self, |target, token| match target {
Value::Object(map) => map.get(&token),
Value::Array(list) => parse_index(&token).and_then(|x| list.get(x)),
_ => 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](
https://tools.ietf.org/html/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 pointer_mut(&mut self, pointer: &str) -> Option<&mut Value> {
if pointer.is_empty() {
return Some(self);
}
if !pointer.starts_with('/') {
return None;
}
pointer
.split('/')
.skip(1)
.map(|x| x.replace("~1", "/").replace("~0", "~"))
.try_fold(self, |target, token| match target {
Value::Object(map) => map.get_mut(&token),
Value::Array(list) => parse_index(&token).and_then(move |x| list.get_mut(x)),
_ => None,
})
}
/// Takes the value out of the `Value`, leaving a `Null` in its place.
///
/// ```
/// # use serde_json::json;
/// #
/// let mut v = json!({ "x": "y" });
/// assert_eq!(v["x"].take(), json!("y"));
/// assert_eq!(v, json!({ "x": null }));
/// ```
pub fn take(&mut self) -> Value {
mem::replace(self, Value::Null)
}
}
/// The default value is `Value::Null`.
///
/// This is useful for handling omitted `Value` fields when deserializing.
///
/// # Examples
///
/// ```
/// # use serde::Deserialize;
/// use serde_json::Value;
///
/// #[derive(Deserialize)]
/// struct Settings {
/// level: i32,
/// #[serde(default)]
/// extras: Value,
/// }
///
/// # fn try_main() -> Result<(), serde_json::Error> {
/// let data = r#" { "level": 42 } "#;
/// let s: Settings = serde_json::from_str(data)?;
///
/// assert_eq!(s.level, 42);
/// assert_eq!(s.extras, Value::Null);
/// #
/// # Ok(())
/// # }
/// #
/// # try_main().unwrap()
/// ```
impl Default for Value {
fn default() -> Value {
Value::Null
}
}
mod de;
mod from;
mod index;
mod partial_eq;
mod ser;
/// Convert a `T` into `serde_json::Value` which is an enum that can represent
/// any valid JSON data.
///
/// # Example
///
/// ```
/// use serde::Serialize;
/// use serde_json::json;
/// use std::error::Error;
///
/// #[derive(Serialize)]
/// struct User {
/// fingerprint: String,
/// location: String,
/// }
///
/// fn compare_json_values() -> Result<(), Box<dyn Error>> {
/// let u = User {
/// fingerprint: "0xF9BA143B95FF6D82".to_owned(),
/// location: "Menlo Park, CA".to_owned(),
/// };
///
/// // The type of `expected` is `serde_json::Value`
/// let expected = json!({
/// "fingerprint": "0xF9BA143B95FF6D82",
/// "location": "Menlo Park, CA",
/// });
///
/// let v = serde_json::to_value(u).unwrap();
/// assert_eq!(v, expected);
///
/// Ok(())
/// }
/// #
/// # compare_json_values().unwrap();
/// ```
///
/// # Errors
///
/// This conversion can fail if `T`'s implementation of `Serialize` decides to
/// fail, or if `T` contains a map with non-string keys.
///
/// ```
/// use std::collections::BTreeMap;
///
/// fn main() {
/// // The keys in this map are vectors, not strings.
/// let mut map = BTreeMap::new();
/// map.insert(vec![32, 64], "x86");
///
/// println!("{}", serde_json::to_value(map).unwrap_err());
/// }
/// ```
// Taking by value is more friendly to iterator adapters, option and result
// consumers, etc. See
https://github.com/serde-rs/json/pull/149.
pub fn to_value<T>(value: T) -> Result<Value, Error>
where
T: Serialize,
{
value.serialize(Serializer)
}
/// Interpret a `serde_json::Value` as an instance of type `T`.
///
/// # Example
///
/// ```
/// use serde::Deserialize;
/// use serde_json::json;
///
/// #[derive(Deserialize, Debug)]
/// struct User {
/// fingerprint: String,
/// location: String,
/// }
///
/// fn main() {
/// // The type of `j` is `serde_json::Value`
/// let j = json!({
/// "fingerprint": "0xF9BA143B95FF6D82",
/// "location": "Menlo Park, CA"
/// });
///
/// let u: User = serde_json::from_value(j).unwrap();
/// println!("{:#?}", u);
/// }
/// ```
///
/// # Errors
///
/// This conversion can fail if the structure of the Value does not match the
/// structure expected by `T`, for example if `T` is a struct type but the Value
/// contains something other than a JSON map. It can also fail if the structure
/// is correct but `T`'s implementation of `Deserialize` decides that something
/// is wrong with the data, for example required struct fields are missing from
/// the JSON map or some number is too big to fit in the expected primitive
/// type.
pub fn from_value<T>(value: Value) -> Result<T, Error>
where
T: DeserializeOwned,
{
T::deserialize(value)
}
