New upstream version 1.18.0+dfsg1

[rustc.git] / src / vendor / serde_json / src / value.rs

//! 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. In order to use this macro,
//! `serde_json` needs to be imported with the `#[macro_use]` attribute.
//!
//! ```rust
//! #[macro_use]
//! extern crate serde_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.
//!
//! ```rust
//! # #[macro_use] extern crate serde_json;
//! # fn random_phone() -> u16 { 0 }
//! # fn main() {
//! 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())
//!   ]
//! });
//! # let _ = john;
//! # }
//! ```
//!
//! 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],
//! [`from_iter`][from_iter] for parsing from an iterator of bytes, and
//! [`from_reader`][from_reader] for parsing from any `io::Read` like a File or
//! a TCP stream.
//!
//! ```rust
//! # extern crate serde_json;
//! # use serde_json::Error;
//! # pub fn example() -> Result<(), Error> {
//! use serde_json::Value;
//!
//! let data = r#" { "name": "John Doe", "age": 43, ... } "#;
//! let v: Value = serde_json::from_str(data)?;
//! println!("Please call {} at the number {}", v["name"], v["phones"][0]);
//! # Ok(()) }
//! # fn main() {}
//! ```
//!
//! [macro]: https://docs.serde.rs/serde_json/macro.json.html
//! [from_str]: https://docs.serde.rs/serde_json/de/fn.from_str.html
//! [from_slice]: https://docs.serde.rs/serde_json/de/fn.from_slice.html
//! [from_iter]: https://docs.serde.rs/serde_json/de/fn.from_iter.html
//! [from_reader]: https://docs.serde.rs/serde_json/de/fn.from_reader.html

use std::fmt;
use std::i64;
use std::io;
use std::ops;
use std::slice;
use std::str;
use std::vec;
use std::borrow::Cow;

use serde::de::{self, Unexpected};
use serde::ser;
use serde::de::value::ValueDeserializer;

use error::{Error, ErrorCode};

pub use map::Map;
pub use number::Number;

/// Represents any valid JSON value.
#[derive(Debug, Clone, PartialEq)]
pub enum Value {
    /// Represents a JSON null value.
    Null,

    /// Represents a JSON boolean.
    Bool(bool),

    /// Represents a JSON number, whether integer or floating point.
    Number(Number),

    /// Represents a JSON string.
    String(String),

    /// Represents a JSON array.
    Array(Vec<Value>),

    /// Represents a JSON object.
    Object(Map<String, Value>),
}

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.
    ///
    /// ```rust
    /// # #[macro_use] extern crate serde_json;
    /// # fn main() {
    /// 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`.
    ///
    /// ```rust
    /// # #[macro_use] extern crate serde_json;
    /// # fn main() {
    /// 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.
    ///
    /// ```rust
    /// # #[macro_use] extern crate serde_json;
    /// # fn main() {
    /// 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.
    pub fn is_object(&self) -> bool {
        self.as_object().is_some()
    }

    /// If the `Value` is an Object, returns the associated Map.
    /// Returns None otherwise.
    pub fn as_object(&self) -> Option<&Map<String, Value>> {
        match *self {
            Value::Object(ref map) => Some(map),
            _ => None,
        }
    }

    /// If the `Value` is an Object, returns the associated mutable Map.
    /// Returns None otherwise.
    pub fn as_object_mut(&mut self) -> Option<&mut Map<String, Value>> {
        match *self {
            Value::Object(ref mut map) => Some(map),
            _ => None,
        }
    }

    /// Returns true if the `Value` is an Array. Returns false otherwise.
    pub fn is_array(&self) -> bool {
        self.as_array().is_some()
    }

    /// If the `Value` is an Array, returns the associated vector.
    /// Returns None otherwise.
    pub fn as_array(&self) -> Option<&Vec<Value>> {
        match *self {
            Value::Array(ref array) => Some(&*array),
            _ => None,
        }
    }

    /// If the `Value` is an Array, returns the associated mutable vector.
    /// Returns None otherwise.
    pub fn as_array_mut(&mut self) -> Option<&mut Vec<Value>> {
        match *self {
            Value::Array(ref mut list) => Some(list),
            _ => None,
        }
    }

    /// Returns true if the `Value` is a String. Returns false otherwise.
    pub fn is_string(&self) -> bool {
        self.as_str().is_some()
    }

    /// If the `Value` is a String, returns the associated str.
    /// Returns None otherwise.
    pub fn as_str(&self) -> Option<&str> {
        match *self {
            Value::String(ref s) => Some(s),
            _ => None,
        }
    }

    /// Returns true if the `Value` is a Number. Returns false otherwise.
    pub fn is_number(&self) -> bool {
        match *self {
            Value::Number(_) => true,
            _ => false,
        }
    }

    /// Returns true if the `Value` is a number that can be represented by i64.
    pub fn is_i64(&self) -> bool {
        match *self {
            Value::Number(ref n) => n.is_i64(),
            _ => false,
        }
    }

    /// Returns true if the `Value` is a number that can be represented by u64.
    pub fn is_u64(&self) -> bool {
        match *self {
            Value::Number(ref n) => n.is_u64(),
            _ => false,
        }
    }

    /// Returns true if the `Value` is a number that can be represented by f64.
    pub fn is_f64(&self) -> bool {
        match *self {
            Value::Number(ref n) => n.is_f64(),
            _ => false,
        }
    }

    /// If the `Value` is a number, represent it as i64 if possible.
    /// Returns None otherwise.
    pub fn as_i64(&self) -> Option<i64> {
        match *self {
            Value::Number(ref n) => n.as_i64(),
            _ => None,
        }
    }

    /// If the `Value` is a number, represent it as u64 if possible.
    /// Returns None otherwise.
    pub fn as_u64(&self) -> Option<u64> {
        match *self {
            Value::Number(ref n) => n.as_u64(),
            _ => None,
        }
    }

    /// If the `Value` is a number, represent it as f64 if possible.
    /// Returns None otherwise.
    pub fn as_f64(&self) -> Option<f64> {
        match *self {
            Value::Number(ref n) => n.as_f64(),
            _ => None,
        }
    }

    /// Returns true if the `Value` is a Boolean. Returns false otherwise.
    pub fn is_boolean(&self) -> bool {
        self.as_bool().is_some()
    }

    /// If the `Value` is a Boolean, returns the associated bool.
    /// Returns None otherwise.
    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.
    pub fn is_null(&self) -> bool {
        self.as_null().is_some()
    }

    /// If the `Value` is a Null, returns ().
    /// Returns None otherwise.
    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
    ///
    /// ```rust
    /// # #[macro_use] extern crate serde_json;
    /// # fn main() {
    /// 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<'a>(&'a self, pointer: &str) -> Option<&'a Value> {
        if pointer == "" {
            return Some(self);
        }
        if !pointer.starts_with('/') {
            return None;
        }
        let tokens = pointer.split('/').skip(1).map(|x| x.replace("~1", "/").replace("~0", "~"));
        let mut target = self;

        for token in tokens {
            let target_opt = match *target {
                Value::Object(ref map) => map.get(&token),
                Value::Array(ref list) => parse_index(&token).and_then(|x| list.get(x)),
                _ => return None,
            };
            if let Some(t) = target_opt {
                target = t;
            } else {
                return None;
            }
        }
        Some(target)
    }

    /// 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
    ///
    /// ```rust
    /// extern crate serde_json;
    ///
    /// use serde_json::Value;
    /// use std::mem;
    ///
    /// 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()));
    ///
    ///     // "Steal" ownership of a value. Can replace with any valid Value.
    ///     let old_x = value.pointer_mut("/x").map(|x| mem::replace(x, Value::Null)).unwrap();
    ///     assert_eq!(old_x, 1.5);
    ///     assert_eq!(value.pointer("/x").unwrap(), &Value::Null);
    /// }
    /// ```
    pub fn pointer_mut<'a>(&'a mut self, pointer: &str) -> Option<&'a mut Value> {
        if pointer == "" {
            return Some(self);
        }
        if !pointer.starts_with('/') {
            return None;
        }
        let tokens = pointer.split('/').skip(1).map(|x| x.replace("~1", "/").replace("~0", "~"));
        let mut target = self;

        for token in tokens {
            // borrow checker gets confused about `target` being mutably borrowed too many times because of the loop
            // this once-per-loop binding makes the scope clearer and circumvents the error
            let target_once = target;
            let target_opt = match *target_once {
                Value::Object(ref mut map) => map.get_mut(&token),
                Value::Array(ref mut list) => parse_index(&token).and_then(move |x| list.get_mut(x)),
                _ => return None,
            };
            if let Some(t) = target_opt {
                target = t;
            } else {
                return None;
            }
        }
        Some(target)
    }
}

/// The default value is `Value::Null`.
///
/// This is useful for handling omitted `Value` fields when deserializing.
///
/// # Examples
///
/// ```rust
/// # extern crate serde_json;
/// # #[macro_use] extern crate serde_derive;
/// use serde_json::Value;
///
/// #[derive(Deserialize)]
/// struct Settings {
///     level: i32,
///     #[serde(default)]
///     extras: Value,
/// }
///
/// # pub 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(()) }
/// # fn main() { try_main().unwrap() }
/// ```
impl Default for Value {
    fn default() -> Value {
        Value::Null
    }
}

/// A type that can be used to index into a `serde_json::Value`. See the `get`
/// and `get_mut` methods of `Value`.
///
/// This trait is sealed and cannot be implemented for types outside of
/// `serde_json`.
pub trait Index: private::Sealed {
    /// Return None if the key is not already in the array or object.
    #[doc(hidden)]
    fn index_into<'v>(&self, v: &'v Value) -> Option<&'v Value>;

    /// Return None if the key is not already in the array or object.
    #[doc(hidden)]
    fn index_into_mut<'v>(&self, v: &'v mut Value) -> Option<&'v mut Value>;

    /// Panic if array index out of bounds. If key is not already in the object,
    /// insert it with a value of null. Panic if Value is a type that cannot be
    /// indexed into, except if Value is null then it can be treated as an empty
    /// object.
    #[doc(hidden)]
    fn index_or_insert<'v>(&self, v: &'v mut Value) -> &'v mut Value;
}

impl Index for usize {
    fn index_into<'v>(&self, v: &'v Value) -> Option<&'v Value> {
        match *v {
            Value::Array(ref vec) => vec.get(*self),
            _ => None,
        }
    }
    fn index_into_mut<'v>(&self, v: &'v mut Value) -> Option<&'v mut Value> {
        match *v {
            Value::Array(ref mut vec) => vec.get_mut(*self),
            _ => None,
        }
    }
    fn index_or_insert<'v>(&self, v: &'v mut Value) -> &'v mut Value {
        match *v {
            Value::Array(ref mut vec) => {
                let len = vec.len();
                vec.get_mut(*self).unwrap_or_else(|| {
                    panic!("cannot access index {} of JSON array of length {}",
                           self, len)
                })
            }
            _ => panic!("cannot access index {} of JSON {}", self, Type(v)),
        }
    }
}

impl Index for str {
    fn index_into<'v>(&self, v: &'v Value) -> Option<&'v Value> {
        match *v {
            Value::Object(ref map) => map.get(self),
            _ => None,
        }
    }
    fn index_into_mut<'v>(&self, v: &'v mut Value) -> Option<&'v mut Value> {
        match *v {
            Value::Object(ref mut map) => map.get_mut(self),
            _ => None,
        }
    }
    fn index_or_insert<'v>(&self, v: &'v mut Value) -> &'v mut Value {
        if let Value::Null = *v {
            let mut map = Map::new();
            map.insert(self.to_owned(), Value::Null);
            *v = Value::Object(map);
        }
        match *v {
            Value::Object(ref mut map) => {
                // TODO: use entry() once LinkedHashMap supports entry()
                // https://github.com/contain-rs/linked-hash-map/issues/5
                if !map.contains_key(self) {
                    map.insert(self.to_owned(), Value::Null);
                }
                map.get_mut(self).unwrap()
            }
            _ => panic!("cannot access key {:?} in JSON {}", self, Type(v)),
        }
    }
}

impl Index for String {
    fn index_into<'v>(&self, v: &'v Value) -> Option<&'v Value> {
        self[..].index_into(v)
    }
    fn index_into_mut<'v>(&self, v: &'v mut Value) -> Option<&'v mut Value> {
        self[..].index_into_mut(v)
    }
    fn index_or_insert<'v>(&self, v: &'v mut Value) -> &'v mut Value {
        self[..].index_or_insert(v)
    }
}

impl<'a, T: ?Sized> Index for &'a T where T: Index {
    fn index_into<'v>(&self, v: &'v Value) -> Option<&'v Value> {
        (**self).index_into(v)
    }
    fn index_into_mut<'v>(&self, v: &'v mut Value) -> Option<&'v mut Value> {
        (**self).index_into_mut(v)
    }
    fn index_or_insert<'v>(&self, v: &'v mut Value) -> &'v mut Value {
        (**self).index_or_insert(v)
    }
}

// Prevent users from implementing the Index trait.
mod private {
    pub trait Sealed {}
    impl Sealed for usize {}
    impl Sealed for str {}
    impl Sealed for String {}
    impl<'a, T: ?Sized> Sealed for &'a T where T: Sealed {}
}

/// Used in panic messages.
struct Type<'a>(&'a Value);

impl<'a> fmt::Display for Type<'a> {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        match *self.0 {
            Value::Null => formatter.write_str("null"),
            Value::Bool(_) => formatter.write_str("boolean"),
            Value::Number(_) => formatter.write_str("number"),
            Value::String(_) => formatter.write_str("string"),
            Value::Array(_) => formatter.write_str("array"),
            Value::Object(_) => formatter.write_str("object"),
        }
    }
}

// The usual semantics of Index is to panic on invalid indexing.
//
// That said, the usual semantics are for things like Vec and BTreeMap which
// have different use cases than Value. If you are working with a Vec, you know
// that you are working with a Vec and you can get the len of the Vec and make
// sure your indices are within bounds. The Value use cases are more
// loosey-goosey. You got some JSON from an endpoint and you want to pull values
// out of it. Outside of this Index impl, you already have the option of using
// value.as_array() and working with the Vec directly, or matching on
// Value::Array and getting the Vec directly. The Index impl means you can skip
// that and index directly into the thing using a concise syntax. You don't have
// to check the type, you don't have to check the len, it is all about what you
// expect the Value to look like.
//
// Basically the use cases that would be well served by panicking here are
// better served by using one of the other approaches: get and get_mut,
// as_array, or match. The value of this impl is that it adds a way of working
// with Value that is not well served by the existing approaches: concise and
// careless and sometimes that is exactly what you want.
impl<I> ops::Index<I> for Value where I: Index {
    type Output = Value;

    /// Index into a `serde_json::Value` using the syntax `value[0]` or
    /// `value["k"]`.
    ///
    /// Returns `Value::Null` 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 `Value::Null` if the given key does not exist
    /// in the map or the given index is not within the bounds of the array.
    ///
    /// For retrieving deeply nested values, you should have a look at the
    /// `Value::pointer` method.
    ///
    /// # Examples
    ///
    /// ```rust
    /// # #[macro_use] extern crate serde_json;
    /// # fn main() {
    /// 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
    /// # }
    /// ```
    fn index(&self, index: I) -> &Value {
        static NULL: Value = Value::Null;
        index.index_into(self).unwrap_or(&NULL)
    }
}

impl<I> ops::IndexMut<I> for Value where I: Index {
    /// Write into a `serde_json::Value` using the syntax `value[0] = ...` or
    /// `value["k"] = ...`.
    ///
    /// If the index is a number, the value must be an array of length bigger
    /// than the index. Indexing into a value that is not an array or an array
    /// that is too small will panic.
    ///
    /// If the index is a string, the value must be an object or null which is
    /// treated like an empty object. If the key is not already present in the
    /// object, it will be inserted with a value of null. Indexing into a value
    /// that is neither an object nor null will panic.
    ///
    /// # Examples
    ///
    /// ```rust
    /// # #[macro_use] extern crate serde_json;
    /// # fn main() {
    /// 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);
    /// # }
    /// ```
    fn index_mut(&mut self, index: I) -> &mut Value {
        index.index_or_insert(self)
    }
}

impl PartialEq<str> for Value {
    fn eq(&self, other: &str) -> bool {
        self.as_str().map_or(false, |s| s == other)
    }
}

impl<'a> PartialEq<&'a str> for Value {
    fn eq(&self, other: &&str) -> bool {
        self.as_str().map_or(false, |s| s == *other)
    }
}

impl PartialEq<Value> for str {
    fn eq(&self, other: &Value) -> bool {
        other.as_str().map_or(false, |s| s == self)
    }
}

impl<'a> PartialEq<Value> for &'a str {
    fn eq(&self, other: &Value) -> bool {
        other.as_str().map_or(false, |s| s == *self)
    }
}

impl PartialEq<String> for Value {
    fn eq(&self, other: &String) -> bool {
        self.as_str().map_or(false, |s| s == other)
    }
}


impl PartialEq<Value> for String {
    fn eq(&self, other: &Value) -> bool {
        other.as_str().map_or(false, |s| s == self)
    }
}

macro_rules! partialeq_numeric {
    ($([$($ty:ty)*], $conversion:ident, $base:ty)*) => {
        $($(
            impl PartialEq<$ty> for Value {
                fn eq(&self, other: &$ty) -> bool {
                    self.$conversion().map_or(false, |i| i == (*other as $base))
                }
            }

            impl PartialEq<Value> for $ty {
                fn eq(&self, other: &Value) -> bool {
                    other.$conversion().map_or(false, |i| i == (*self as $base))
                }
            }

            impl<'a> PartialEq<$ty> for &'a Value {
                fn eq(&self, other: &$ty) -> bool {
                    self.$conversion().map_or(false, |i| i == (*other as $base))
                }
            }

            impl<'a> PartialEq<$ty> for &'a mut Value {
                fn eq(&self, other: &$ty) -> bool {
                    self.$conversion().map_or(false, |i| i == (*other as $base))
                }
            }
        )*)*
    }
}

partialeq_numeric! {
    [i8 i16 i32 i64 isize], as_i64, i64
    [u8 u16 u32 u64 usize], as_u64, u64
    [f32 f64], as_f64, f64
}

macro_rules! from_integer {
    ($($ty:ident)*) => {
        $(
            impl From<$ty> for Value {
                fn from(n: $ty) -> Self {
                    Value::Number(n.into())
                }
            }
        )*
    };
}

from_integer! {
    i8 i16 i32 i64 isize
    u8 u16 u32 u64 usize
}

impl From<f32> for Value {
    /// Convert 32-bit floating point number to `Value`
    ///
    /// # Examples
    ///
    /// ```rust
    /// # extern crate serde_json;
    /// use serde_json::Value;
    ///
    /// # fn main() {
    /// let f: f32 = 13.37;
    /// let x: Value = f.into();
    /// # }
    /// ```
    fn from(f: f32) -> Self {
        From::from(f as f64)
    }
}

impl From<f64> for Value {
    /// Convert 64-bit floating point number to `Value`
    ///
    /// # Examples
    ///
    /// ```rust
    /// # extern crate serde_json;
    /// use serde_json::Value;
    ///
    /// # fn main() {
    /// let f: f64 = 13.37;
    /// let x: Value = f.into();
    /// # }
    /// ```
    fn from(f: f64) -> Self {
        Number::from_f64(f).map_or(Value::Null, Value::Number)
    }
}

impl From<bool> for Value {
    /// Convert boolean to `Value`
    ///
    /// # Examples
    ///
    /// ```rust
    /// # extern crate serde_json;
    /// use serde_json::Value;
    ///
    /// # fn main() {
    /// let b = false;
    /// let x: Value = b.into();
    /// # }
    /// ```
    fn from(f: bool) -> Self {
        Value::Bool(f)
    }
}

impl From<String> for Value {
    /// Convert `String` to `Value`
    ///
    /// # Examples
    ///
    /// ```rust
    /// # extern crate serde_json;
    /// use serde_json::Value;
    ///
    /// # fn main() {
    /// let s: String = "lorem".to_string();
    /// let x: Value = s.into();
    /// # }
    /// ```
    fn from(f: String) -> Self {
        Value::String(f)
    }
}

impl<'a> From<&'a str> for Value {
    /// Convert string slice to `Value`
    ///
    /// # Examples
    ///
    /// ```rust
    /// # extern crate serde_json;
    /// use serde_json::Value;
    ///
    /// # fn main() {
    /// let s: &str = "lorem";
    /// let x: Value = s.into();
    /// # }
    /// ```
    fn from(f: &str) -> Self {
        Value::String(f.to_string())
    }
}

impl<'a> From<Cow<'a, str>> for Value {
    /// Convert copy-on-write string to `Value`
    ///
    /// # Examples
    ///
    /// ```rust
    /// # extern crate serde_json;
    /// use serde_json::Value;
    /// use std::borrow::Cow;
    /// # fn main() {
    ///
    /// let s: Cow<str> = Cow::Borrowed("lorem");
    /// let x: Value = s.into();
    /// # }
    /// ```
    ///
    /// ```rust
    /// # extern crate serde_json;
    /// use serde_json::Value;
    /// use std::borrow::Cow;
    ///
    /// # fn main() {
    /// let s: Cow<str> = Cow::Owned("lorem".to_string());
    /// let x: Value = s.into();
    /// # }
    /// ```
    fn from(f: Cow<'a, str>) -> Self {
        Value::String(f.to_string())
    }
}

impl From<Map<String, Value>> for Value {
    /// Convert map (with string keys) to `Value`
    ///
    /// # Examples
    ///
    /// ```rust
    /// # extern crate serde_json;
    /// use serde_json::{Map, Value};
    /// # fn main() {
    ///
    /// let mut m = Map::new();
    /// m.insert("Lorem".to_string(), "ipsum".into());
    /// let x: Value = m.into();
    /// # }
    /// ```
    fn from(f: Map<String, Value>) -> Self {
        Value::Object(f)
    }
}

impl<T: Into<Value>> From<Vec<T>> for Value {
    /// Convert a `Vec` to `Value`
    ///
    /// # Examples
    ///
    /// ```rust
    /// # extern crate serde_json;
    /// use serde_json::Value;
    /// # fn main() {
    ///
    /// let v = vec!["lorem", "ipsum", "dolor"];
    /// let x: Value = v.into();
    /// # }
    /// ```
    fn from(f: Vec<T>) -> Self {
        Value::Array(f.into_iter().map(Into::into).collect())
    }
}

impl<'a, T: Clone + Into<Value>> From<&'a [T]> for Value {
    /// Convert a slice to `Value`
    ///
    /// # Examples
    ///
    /// ```rust
    /// # extern crate serde_json;
    /// use serde_json::Value;
    /// # fn main() {
    ///
    /// let v: &[&str] = &["lorem", "ipsum", "dolor"];
    /// let x: Value = v.into();
    /// # }
    /// ```
    fn from(f: &'a [T]) -> Self {
        Value::Array(f.into_iter().cloned().map(Into::into).collect())
    }
}

impl<T: Into<Value>> ::std::iter::FromIterator<T> for Value {
    /// Convert an iteratable type to a `Value`
    ///
    /// # Examples
    ///
    /// ```rust
    /// # extern crate serde_json;
    /// use serde_json::Value;
    /// # fn main() {
    ///
    /// let v = std::iter::repeat(42).take(5);
    /// let x: Value = v.collect();
    /// # }
    /// ```
    ///
    /// ```rust
    /// # extern crate serde_json;
    /// use serde_json::Value;
    ///
    /// # fn main() {
    /// let v: Vec<_> = vec!["lorem", "ipsum", "dolor"];
    /// let x: Value = v.into_iter().collect();
    /// # }
    /// ```
    ///
    /// ```rust
    /// # extern crate serde_json;
    /// use std::iter::FromIterator;
    /// use serde_json::Value;
    ///
    /// # fn main() {
    /// let x: Value = Value::from_iter(vec!["lorem", "ipsum", "dolor"]);
    /// # }
    /// ```
    fn from_iter<I: IntoIterator<Item=T>>(iter: I) -> Self {
        let vec: Vec<Value> = iter.into_iter().map(|x| x.into()).collect();

        Value::Array(vec)
    }
}

impl ser::Serialize for Value {
    #[inline]
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
        where S: ser::Serializer,
    {
        match *self {
            Value::Null => serializer.serialize_unit(),
            Value::Bool(b) => serializer.serialize_bool(b),
            Value::Number(ref n) => n.serialize(serializer),
            Value::String(ref s) => serializer.serialize_str(s),
            Value::Array(ref v) => v.serialize(serializer),
            Value::Object(ref m) => {
                use serde::ser::SerializeMap;
                let mut map = try!(serializer.serialize_map(Some(m.len())));
                for (k, v) in m {
                    try!(map.serialize_key(k));
                    try!(map.serialize_value(v));
                }
                map.end()
            }
        }
    }
}

impl de::Deserialize for Value {
    #[inline]
    fn deserialize<D>(deserializer: D) -> Result<Value, D::Error>
        where D: de::Deserializer,
    {
        struct ValueVisitor;

        impl de::Visitor for ValueVisitor {
            type Value = Value;

            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
                formatter.write_str("any valid JSON value")
            }

            #[inline]
            fn visit_bool<E>(self, value: bool) -> Result<Value, E> {
                Ok(Value::Bool(value))
            }

            #[inline]
            fn visit_i64<E>(self, value: i64) -> Result<Value, E> {
                Ok(Value::Number(value.into()))
            }

            #[inline]
            fn visit_u64<E>(self, value: u64) -> Result<Value, E> {
                Ok(Value::Number(value.into()))
            }

            #[inline]
            fn visit_f64<E>(self, value: f64) -> Result<Value, E> {
                Ok(Number::from_f64(value).map_or(Value::Null, Value::Number))
            }

            #[inline]
            fn visit_str<E>(self, value: &str) -> Result<Value, E>
                where E: de::Error,
            {
                self.visit_string(String::from(value))
            }

            #[inline]
            fn visit_string<E>(self, value: String) -> Result<Value, E> {
                Ok(Value::String(value))
            }

            #[inline]
            fn visit_none<E>(self) -> Result<Value, E> {
                Ok(Value::Null)
            }

            #[inline]
            fn visit_some<D>(
                self,
                deserializer: D
            ) -> Result<Value, D::Error>
                where D: de::Deserializer,
            {
                de::Deserialize::deserialize(deserializer)
            }

            #[inline]
            fn visit_unit<E>(self) -> Result<Value, E> {
                Ok(Value::Null)
            }

            #[inline]
            fn visit_seq<V>(self, visitor: V) -> Result<Value, V::Error>
                where V: de::SeqVisitor,
            {
                let values = try!(de::impls::VecVisitor::new()
                    .visit_seq(visitor));
                Ok(Value::Array(values))
            }

            fn visit_map<V>(self, mut visitor: V) -> Result<Value, V::Error>
                where V: de::MapVisitor,
            {
                let mut values = Map::with_capacity(visitor.size_hint().0);

                while let Some((key, value)) = try!(visitor.visit()) {
                    values.insert(key, value);
                }

                Ok(Value::Object(values))
            }
        }

        deserializer.deserialize(ValueVisitor)
    }
}

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> {
        fn io_error<E>(_: E) -> io::Error {
            // Value does not matter because fmt::Debug and fmt::Display impls
            // below just map it to fmt::Error
            io::Error::new(io::ErrorKind::Other, "fmt error")
        }
        let s = try!(str::from_utf8(buf).map_err(io_error));
        try!(self.inner.write_str(s).map_err(io_error));
        Ok(buf.len())
    }

    fn flush(&mut self) -> io::Result<()> {
        Ok(())
    }
}

impl fmt::Display for Value {
    /// Serializes a json value into a string
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let mut wr = WriterFormatter {
            inner: f,
        };
        super::ser::to_writer(&mut wr, self).map_err(|_| fmt::Error)
    }
}

impl str::FromStr for Value {
    type Err = Error;
    fn from_str(s: &str) -> Result<Value, Error> {
        super::de::from_str(s)
    }
}

struct Serializer;

impl ser::Serializer for Serializer {
    type Ok = Value;
    type Error = Error;

    type SerializeSeq = SerializeVec;
    type SerializeTuple = SerializeVec;
    type SerializeTupleStruct = SerializeVec;
    type SerializeTupleVariant = SerializeTupleVariant;
    type SerializeMap = SerializeMap;
    type SerializeStruct = SerializeMap;
    type SerializeStructVariant = SerializeStructVariant;

    #[inline]
    fn serialize_bool(self, value: bool) -> Result<Value, Error> {
        Ok(Value::Bool(value))
    }

    #[inline]
    fn serialize_i8(self, value: i8) -> Result<Value, Error> {
        self.serialize_i64(value as i64)
    }

    #[inline]
    fn serialize_i16(self, value: i16) -> Result<Value, Error> {
        self.serialize_i64(value as i64)
    }

    #[inline]
    fn serialize_i32(self, value: i32) -> Result<Value, Error> {
        self.serialize_i64(value as i64)
    }

    fn serialize_i64(self, value: i64) -> Result<Value, Error> {
        Ok(Value::Number(value.into()))
    }

    #[inline]
    fn serialize_u8(self, value: u8) -> Result<Value, Error> {
        self.serialize_u64(value as u64)
    }

    #[inline]
    fn serialize_u16(self, value: u16) -> Result<Value, Error> {
        self.serialize_u64(value as u64)
    }

    #[inline]
    fn serialize_u32(self, value: u32) -> Result<Value, Error> {
        self.serialize_u64(value as u64)
    }

    #[inline]
    fn serialize_u64(self, value: u64) -> Result<Value, Error> {
        Ok(Value::Number(value.into()))
    }

    #[inline]
    fn serialize_f32(self, value: f32) -> Result<Value, Error> {
        self.serialize_f64(value as f64)
    }

    #[inline]
    fn serialize_f64(self, value: f64) -> Result<Value, Error> {
        Ok(Number::from_f64(value).map_or(Value::Null, Value::Number))
    }

    #[inline]
    fn serialize_char(self, value: char) -> Result<Value, Error> {
        let mut s = String::new();
        s.push(value);
        self.serialize_str(&s)
    }

    #[inline]
    fn serialize_str(self, value: &str) -> Result<Value, Error> {
        Ok(Value::String(value.to_owned()))
    }

    fn serialize_bytes(self, value: &[u8]) -> Result<Value, Error> {
        let vec = value.iter().map(|&b| Value::Number(b.into())).collect();
        Ok(Value::Array(vec))
    }

    #[inline]
    fn serialize_unit(self) -> Result<Value, Error> {
        Ok(Value::Null)
    }

    #[inline]
    fn serialize_unit_struct(
        self,
        _name: &'static str
    ) -> Result<Value, Error> {
        self.serialize_unit()
    }

    #[inline]
    fn serialize_unit_variant(
        self,
        _name: &'static str,
        _variant_index: usize,
        variant: &'static str
    ) -> Result<Value, Error> {
        self.serialize_str(variant)
    }

    #[inline]
    fn serialize_newtype_struct<T: ?Sized>(
        self,
        _name: &'static str,
        value: &T
    ) -> Result<Value, Error>
        where T: ser::Serialize,
    {
        value.serialize(self)
    }

    fn serialize_newtype_variant<T: ?Sized>(
        self,
        _name: &'static str,
        _variant_index: usize,
        variant: &'static str,
        value: &T
    ) -> Result<Value, Error>
        where T: ser::Serialize,
    {
        let mut values = Map::new();
        values.insert(String::from(variant), try!(to_value(&value)));
        Ok(Value::Object(values))
    }

    #[inline]
    fn serialize_none(self) -> Result<Value, Error> {
        self.serialize_unit()
    }

    #[inline]
    fn serialize_some<T: ?Sized>(self, value: &T) -> Result<Value, Error>
        where T: ser::Serialize,
    {
        value.serialize(self)
    }

    fn serialize_seq(
        self,
        len: Option<usize>
    ) -> Result<Self::SerializeSeq, Error> {
        Ok(SerializeVec {
            vec: Vec::with_capacity(len.unwrap_or(0))
        })
    }

    fn serialize_seq_fixed_size(
        self,
        size: usize
    ) -> Result<Self::SerializeSeq, Error> {
        self.serialize_seq(Some(size))
    }

    fn serialize_tuple(self, len: usize) -> Result<Self::SerializeTuple, Error> {
        self.serialize_seq(Some(len))
    }

    fn serialize_tuple_struct(
        self,
        _name: &'static str,
        len: usize
    ) -> Result<Self::SerializeTupleStruct, Error> {
        self.serialize_seq(Some(len))
    }

    fn serialize_tuple_variant(
        self,
        _name: &'static str,
        _variant_index: usize,
        variant: &'static str,
        len: usize
    ) -> Result<Self::SerializeTupleVariant, Error> {
        Ok(SerializeTupleVariant {
            name: String::from(variant),
            vec: Vec::with_capacity(len),
        })
    }

    fn serialize_map(
        self,
        _len: Option<usize>
    ) -> Result<Self::SerializeMap, Error> {
        Ok(SerializeMap {
            map: Map::new(),
            next_key: None,
        })
    }

    fn serialize_struct(
        self,
        _name: &'static str,
        len: usize
    ) -> Result<Self::SerializeStruct, Error> {
        self.serialize_map(Some(len))
    }

    fn serialize_struct_variant(
        self,
        _name: &'static str,
        _variant_index: usize,
        variant: &'static str,
        _len: usize
    ) -> Result<Self::SerializeStructVariant, Error> {
        Ok(SerializeStructVariant {
            name: String::from(variant),
            map: Map::new(),
        })
    }
}

#[doc(hidden)]
pub struct SerializeVec {
    vec: Vec<Value>,
}

#[doc(hidden)]
pub struct SerializeTupleVariant {
    name: String,
    vec: Vec<Value>,
}

#[doc(hidden)]
pub struct SerializeMap {
    map: Map<String, Value>,
    next_key: Option<String>,
}

#[doc(hidden)]
pub struct SerializeStructVariant {
    name: String,
    map: Map<String, Value>,
}

impl ser::SerializeSeq for SerializeVec {
    type Ok = Value;
    type Error = Error;

    fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
        where T: ser::Serialize
    {
        self.vec.push(try!(to_value(&value)));
        Ok(())
    }

    fn end(self) -> Result<Value, Error> {
        Ok(Value::Array(self.vec))
    }
}

impl ser::SerializeTuple for SerializeVec {
    type Ok = Value;
    type Error = Error;

    fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
        where T: ser::Serialize
    {
        ser::SerializeSeq::serialize_element(self, value)
    }

    fn end(self) -> Result<Value, Error> {
        ser::SerializeSeq::end(self)
    }
}

impl ser::SerializeTupleStruct for SerializeVec {
    type Ok = Value;
    type Error = Error;

    fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
        where T: ser::Serialize
    {
        ser::SerializeSeq::serialize_element(self, value)
    }

    fn end(self) -> Result<Value, Error> {
        ser::SerializeSeq::end(self)
    }
}

impl ser::SerializeTupleVariant for SerializeTupleVariant {
    type Ok = Value;
    type Error = Error;

    fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
        where T: ser::Serialize
    {
        self.vec.push(try!(to_value(&value)));
        Ok(())
    }

    fn end(self) -> Result<Value, Error> {
        let mut object = Map::new();

        object.insert(self.name, Value::Array(self.vec));

        Ok(Value::Object(object))
    }
}

impl ser::SerializeMap for SerializeMap {
    type Ok = Value;
    type Error = Error;

    fn serialize_key<T: ?Sized>(&mut self, key: &T) -> Result<(), Error>
        where T: ser::Serialize
    {
        match try!(to_value(&key)) {
            Value::String(s) => self.next_key = Some(s),
            Value::Number(n) => {
                if n.is_u64() || n.is_i64() {
                    self.next_key = Some(n.to_string())
                } else {
                    return Err(Error::syntax(ErrorCode::KeyMustBeAString, 0, 0))
                }
            }
            _ => return Err(Error::syntax(ErrorCode::KeyMustBeAString, 0, 0)),
        };
        Ok(())
    }

    fn serialize_value<T: ?Sized>(&mut self, value: &T) -> Result<(), Error>
        where T: ser::Serialize
    {
        let key = self.next_key.take();
        // Panic because this indicates a bug in the program rather than an
        // expected failure.
        let key = key.expect("serialize_value called before serialize_key");
        self.map.insert(key, try!(to_value(&value)));
        Ok(())
    }

    fn end(self) -> Result<Value, Error> {
        Ok(Value::Object(self.map))
    }
}

impl ser::SerializeStruct for SerializeMap {
    type Ok = Value;
    type Error = Error;

    fn serialize_field<T: ?Sized>(&mut self, key: &'static str, value: &T) -> Result<(), Error>
        where T: ser::Serialize
    {
        try!(ser::SerializeMap::serialize_key(self, key));
        ser::SerializeMap::serialize_value(self, value)
    }

    fn end(self) -> Result<Value, Error> {
        ser::SerializeMap::end(self)
    }
}

impl ser::SerializeStructVariant for SerializeStructVariant {
    type Ok = Value;
    type Error = Error;

    fn serialize_field<T: ?Sized>(&mut self, key: &'static str, value: &T) -> Result<(), Error>
        where T: ser::Serialize
    {
        self.map.insert(String::from(key), try!(to_value(&value)));
        Ok(())
    }

    fn end(self) -> Result<Value, Error> {
        let mut object = Map::new();

        object.insert(self.name, Value::Object(self.map));

        Ok(Value::Object(object))
    }
}

impl de::Deserializer for Value {
    type Error = Error;

    #[inline]
    fn deserialize<V>(self, visitor: V) -> Result<V::Value, Error>
        where V: de::Visitor,
    {
        match self {
            Value::Null => visitor.visit_unit(),
            Value::Bool(v) => visitor.visit_bool(v),
            Value::Number(n) => n.deserialize(visitor),
            Value::String(v) => visitor.visit_string(v),
            Value::Array(v) => {
                let len = v.len();
                let mut deserializer = SeqDeserializer::new(v);
                let seq = try!(visitor.visit_seq(&mut deserializer));
                let remaining = deserializer.iter.len();
                if remaining == 0 {
                    Ok(seq)
                } else {
                    Err(de::Error::invalid_length(len, &"fewer elements in array"))
                }
            }
            Value::Object(v) => {
                let len = v.len();
                let mut deserializer = MapDeserializer::new(v);
                let map = try!(visitor.visit_map(&mut deserializer));
                let remaining = deserializer.iter.len();
                if remaining == 0 {
                    Ok(map)
                } else {
                    Err(de::Error::invalid_length(len, &"fewer elements in map"))
                }
            }
        }
    }

    #[inline]
    fn deserialize_option<V>(
        self,
        visitor: V
    ) -> Result<V::Value, Error>
        where V: de::Visitor,
    {
        match self {
            Value::Null => visitor.visit_none(),
            _ => visitor.visit_some(self),
        }
    }

    #[inline]
    fn deserialize_enum<V>(
        self,
        _name: &str,
        _variants: &'static [&'static str],
        visitor: V
    ) -> Result<V::Value, Error>
        where V: de::Visitor,
    {
        let (variant, value) = match self {
            Value::Object(value) => {
                let mut iter = value.into_iter();
                let (variant, value) = match iter.next() {
                    Some(v) => v,
                    None => {
                        return Err(de::Error::invalid_value(Unexpected::Map, &"map with a single key"));
                    }
                };
                // enums are encoded in json as maps with a single key:value pair
                if iter.next().is_some() {
                    return Err(de::Error::invalid_value(Unexpected::Map, &"map with a single key"));
                }
                (variant, Some(value))
            }
            Value::String(variant) => (variant, None),
            other => {
                return Err(de::Error::invalid_type(other.unexpected(), &"string or map"));
            }
        };

        visitor.visit_enum(EnumDeserializer {
            variant: variant,
            value: value,
        })
    }

    #[inline]
    fn deserialize_newtype_struct<V>(
        self,
        _name: &'static str,
        visitor: V
    ) -> Result<V::Value, Self::Error>
        where V: de::Visitor,
    {
        visitor.visit_newtype_struct(self)
    }

    forward_to_deserialize! {
        bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit seq
        seq_fixed_size bytes byte_buf map unit_struct tuple_struct struct
        struct_field tuple ignored_any
    }
}

struct EnumDeserializer {
    variant: String,
    value: Option<Value>,
}

impl de::EnumVisitor for EnumDeserializer {
    type Error = Error;
    type Variant = VariantDeserializer;

    fn visit_variant_seed<V>(self, seed: V) -> Result<(V::Value, VariantDeserializer), Error>
        where V: de::DeserializeSeed,
    {
        let variant = self.variant.into_deserializer();
        let visitor = VariantDeserializer { value: self.value };
        seed.deserialize(variant).map(|v| (v, visitor))
    }
}

struct VariantDeserializer {
    value: Option<Value>,
}

impl de::VariantVisitor for VariantDeserializer {
    type Error = Error;

    fn visit_unit(self) -> Result<(), Error> {
        match self.value {
            Some(value) => de::Deserialize::deserialize(value),
            None => Ok(()),
        }
    }

    fn visit_newtype_seed<T>(self, seed: T) -> Result<T::Value, Error>
        where T: de::DeserializeSeed,
    {
        match self.value {
            Some(value) => seed.deserialize(value),
            None => Err(de::Error::invalid_type(Unexpected::UnitVariant, &"newtype variant")),
        }
    }

    fn visit_tuple<V>(
        self,
        _len: usize,
        visitor: V
    ) -> Result<V::Value, Error>
        where V: de::Visitor,
    {
        match self.value {
            Some(Value::Array(v)) => {
                de::Deserializer::deserialize(SeqDeserializer::new(v), visitor)
            }
            Some(other) => Err(de::Error::invalid_type(other.unexpected(), &"tuple variant")),
            None => Err(de::Error::invalid_type(Unexpected::UnitVariant, &"tuple variant"))
        }
    }

    fn visit_struct<V>(
        self,
        _fields: &'static [&'static str],
        visitor: V
    ) -> Result<V::Value, Error>
        where V: de::Visitor,
    {
        match self.value {
            Some(Value::Object(v)) => {
                de::Deserializer::deserialize(MapDeserializer::new(v), visitor)
            }
            Some(other) => Err(de::Error::invalid_type(other.unexpected(), &"struct variant")),
            _ => Err(de::Error::invalid_type(Unexpected::UnitVariant, &"struct variant"))
        }
    }
}

struct SeqDeserializer {
    iter: vec::IntoIter<Value>,
}

impl SeqDeserializer {
    fn new(vec: Vec<Value>) -> Self {
        SeqDeserializer {
            iter: vec.into_iter(),
        }
    }
}

impl de::Deserializer for SeqDeserializer {
    type Error = Error;

    #[inline]
    fn deserialize<V>(mut self, visitor: V) -> Result<V::Value, Error>
        where V: de::Visitor,
    {
        let len = self.iter.len();
        if len == 0 {
            visitor.visit_unit()
        } else {
            let ret = try!(visitor.visit_seq(&mut self));
            let remaining = self.iter.len();
            if remaining == 0 {
                Ok(ret)
            } else {
                Err(de::Error::invalid_length(len, &"fewer elements in array"))
            }
        }
    }

    forward_to_deserialize! {
        bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
        seq seq_fixed_size bytes byte_buf map unit_struct newtype_struct
        tuple_struct struct struct_field tuple enum ignored_any
    }
}

impl de::SeqVisitor for SeqDeserializer {
    type Error = Error;

    fn visit_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Error>
        where T: de::DeserializeSeed,
    {
        match self.iter.next() {
            Some(value) => seed.deserialize(value).map(Some),
            None => Ok(None),
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
}

struct MapDeserializer {
    iter: <Map<String, Value> as IntoIterator>::IntoIter,
    value: Option<Value>,
}

impl MapDeserializer {
    fn new(map: Map<String, Value>) -> Self {
        MapDeserializer {
            iter: map.into_iter(),
            value: None,
        }
    }
}

impl de::MapVisitor for MapDeserializer {
    type Error = Error;

    fn visit_key_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Error>
        where T: de::DeserializeSeed,
    {
        match self.iter.next() {
            Some((key, value)) => {
                self.value = Some(value);
                seed.deserialize(key.into_deserializer()).map(Some)
            }
            None => Ok(None),
        }
    }

    fn visit_value_seed<T>(&mut self, seed: T) -> Result<T::Value, Error>
        where T: de::DeserializeSeed,
    {
        match self.value.take() {
            Some(value) => seed.deserialize(value),
            None => Err(de::Error::custom("value is missing")),
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
}

impl de::Deserializer for MapDeserializer {
    type Error = Error;

    #[inline]
    fn deserialize<V>(self, visitor: V) -> Result<V::Value, Error>
        where V: de::Visitor,
    {
        visitor.visit_map(self)
    }

    forward_to_deserialize! {
        bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
        seq seq_fixed_size bytes byte_buf map unit_struct newtype_struct
        tuple_struct struct struct_field tuple enum ignored_any
    }
}

impl<'a> de::Deserializer for &'a Value {
    type Error = Error;

    fn deserialize<V>(self, visitor: V) -> Result<V::Value, Error>
        where V: de::Visitor,
    {
        match *self {
            Value::Null => visitor.visit_unit(),
            Value::Bool(v) => visitor.visit_bool(v),
            Value::Number(ref n) => n.deserialize(visitor),
            Value::String(ref v) => visitor.visit_str(v),
            Value::Array(ref v) => {
                let len = v.len();
                let mut deserializer = SeqRefDeserializer::new(v);
                let seq = try!(visitor.visit_seq(&mut deserializer));
                let remaining = deserializer.iter.len();
                if remaining == 0 {
                    Ok(seq)
                } else {
                    Err(de::Error::invalid_length(len, &"fewer elements in array"))
                }
            }
            Value::Object(ref v) => {
                let len = v.len();
                let mut deserializer = MapRefDeserializer::new(v);
                let map = try!(visitor.visit_map(&mut deserializer));
                let remaining = deserializer.iter.len();
                if remaining == 0 {
                    Ok(map)
                } else {
                    Err(de::Error::invalid_length(len, &"fewer elements in map"))
                }
            }
        }
    }

    fn deserialize_option<V>(
        self,
        visitor: V
    ) -> Result<V::Value, Error>
        where V: de::Visitor,
    {
        match *self {
            Value::Null => visitor.visit_none(),
            _ => visitor.visit_some(self),
        }
    }

    fn deserialize_enum<V>(
        self,
        _name: &str,
        _variants: &'static [&'static str],
        visitor: V
    ) -> Result<V::Value, Error>
        where V: de::Visitor,
    {
        let (variant, value) = match *self {
            Value::Object(ref value) => {
                let mut iter = value.into_iter();
                let (variant, value) = match iter.next() {
                    Some(v) => v,
                    None => {
                        return Err(de::Error::invalid_value(Unexpected::Map, &"map with a single key"));
                    }
                };
                // enums are encoded in json as maps with a single key:value pair
                if iter.next().is_some() {
                    return Err(de::Error::invalid_value(Unexpected::Map, &"map with a single key"));
                }
                (variant, Some(value))
            }
            Value::String(ref variant) => (variant, None),
            ref other => {
                return Err(de::Error::invalid_type(other.unexpected(), &"string or map"));
            }
        };

        visitor.visit_enum(EnumRefDeserializer {
            variant: variant,
            value: value,
        })
    }

    #[inline]
    fn deserialize_newtype_struct<V>(
        self,
        _name: &'static str,
        visitor: V
    ) -> Result<V::Value, Self::Error>
        where V: de::Visitor,
    {
        visitor.visit_newtype_struct(self)
    }

    forward_to_deserialize! {
        bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit seq
        seq_fixed_size bytes byte_buf map unit_struct tuple_struct struct
        struct_field tuple ignored_any
    }
}

struct EnumRefDeserializer<'a> {
    variant: &'a str,
    value: Option<&'a Value>,
}

impl<'a> de::EnumVisitor for EnumRefDeserializer<'a> {
    type Error = Error;
    type Variant = VariantRefDeserializer<'a>;

    fn visit_variant_seed<V>(self, seed: V) -> Result<(V::Value, Self::Variant), Error>
        where V: de::DeserializeSeed,
    {
        let variant = self.variant.into_deserializer();
        let visitor = VariantRefDeserializer { value: self.value };
        seed.deserialize(variant).map(|v| (v, visitor))
    }
}

struct VariantRefDeserializer<'a> {
    value: Option<&'a Value>,
}

impl<'a> de::VariantVisitor for VariantRefDeserializer<'a> {
    type Error = Error;

    fn visit_unit(self) -> Result<(), Error> {
        match self.value {
            Some(value) => de::Deserialize::deserialize(value),
            None => Ok(()),
        }
    }

    fn visit_newtype_seed<T>(self, seed: T) -> Result<T::Value, Error>
        where T: de::DeserializeSeed,
    {
        match self.value {
            Some(value) => seed.deserialize(value),
            None => Err(de::Error::invalid_type(Unexpected::UnitVariant, &"newtype variant")),
        }
    }

    fn visit_tuple<V>(
        self,
        _len: usize,
        visitor: V
    ) -> Result<V::Value, Error>
        where V: de::Visitor,
    {
        match self.value {
            Some(&Value::Array(ref v)) => {
                de::Deserializer::deserialize(SeqRefDeserializer::new(v), visitor)
            }
            Some(other) => Err(de::Error::invalid_type(other.unexpected(), &"tuple variant")),
            None => Err(de::Error::invalid_type(Unexpected::UnitVariant, &"tuple variant"))
        }
    }

    fn visit_struct<V>(
        self,
        _fields: &'static [&'static str],
        visitor: V
    ) -> Result<V::Value, Error>
        where V: de::Visitor,
    {
        match self.value {
            Some(&Value::Object(ref v)) => {
                de::Deserializer::deserialize(MapRefDeserializer::new(v), visitor)
            }
            Some(other) => Err(de::Error::invalid_type(other.unexpected(), &"struct variant")),
            _ => Err(de::Error::invalid_type(Unexpected::UnitVariant, &"struct variant"))
        }
    }
}

struct SeqRefDeserializer<'a> {
    iter: slice::Iter<'a, Value>,
}

impl<'a> SeqRefDeserializer<'a> {
    fn new(slice: &'a [Value]) -> Self {
        SeqRefDeserializer {
            iter: slice.iter(),
        }
    }
}

impl<'a> de::Deserializer for SeqRefDeserializer<'a> {
    type Error = Error;

    #[inline]
    fn deserialize<V>(mut self, visitor: V) -> Result<V::Value, Error>
        where V: de::Visitor,
    {
        let len = self.iter.len();
        if len == 0 {
            visitor.visit_unit()
        } else {
            let ret = try!(visitor.visit_seq(&mut self));
            let remaining = self.iter.len();
            if remaining == 0 {
                Ok(ret)
            } else {
                Err(de::Error::invalid_length(len, &"fewer elements in array"))
            }
        }
    }

    forward_to_deserialize! {
        bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
        seq seq_fixed_size bytes byte_buf map unit_struct newtype_struct
        tuple_struct struct struct_field tuple enum ignored_any
    }
}

impl<'a> de::SeqVisitor for SeqRefDeserializer<'a> {
    type Error = Error;

    fn visit_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Error>
        where T: de::DeserializeSeed,
    {
        match self.iter.next() {
            Some(value) => seed.deserialize(value).map(Some),
            None => Ok(None),
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
}

struct MapRefDeserializer<'a> {
    iter: <&'a Map<String, Value> as IntoIterator>::IntoIter,
    value: Option<&'a Value>,
}

impl<'a> MapRefDeserializer<'a> {
    fn new(map: &'a Map<String, Value>) -> Self {
        MapRefDeserializer {
            iter: map.into_iter(),
            value: None,
        }
    }
}

impl<'a> de::MapVisitor for MapRefDeserializer<'a> {
    type Error = Error;

    fn visit_key_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Error>
        where T: de::DeserializeSeed,
    {
        match self.iter.next() {
            Some((key, value)) => {
                self.value = Some(value);
                seed.deserialize((&**key).into_deserializer()).map(Some)
            }
            None => Ok(None),
        }
    }

    fn visit_value_seed<T>(&mut self, seed: T) -> Result<T::Value, Error>
        where T: de::DeserializeSeed,
    {
        match self.value.take() {
            Some(value) => seed.deserialize(value),
            None => Err(de::Error::custom("value is missing")),
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
}

impl<'a> de::Deserializer for MapRefDeserializer<'a> {
    type Error = Error;

    #[inline]
    fn deserialize<V>(self, visitor: V) -> Result<V::Value, Error>
        where V: de::Visitor,
    {
        visitor.visit_map(self)
    }

    forward_to_deserialize! {
        bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string unit option
        seq seq_fixed_size bytes byte_buf map unit_struct newtype_struct
        tuple_struct struct struct_field tuple enum ignored_any
    }
}

impl Value {
    fn unexpected(&self) -> Unexpected {
        match *self {
            Value::Null => Unexpected::Unit,
            Value::Bool(b) => Unexpected::Bool(b),
            Value::Number(ref n) => {
                if let Some(u) = n.as_u64() {
                    Unexpected::Unsigned(u)
                } else if let Some(i) = n.as_i64() {
                    Unexpected::Signed(i)
                } else if let Some(f) = n.as_f64() {
                    Unexpected::Float(f)
                } else {
                    panic!("unexpected number")
                }
            }
            Value::String(ref s) => Unexpected::Str(s),
            Value::Array(_) => Unexpected::Seq,
            Value::Object(_) => Unexpected::Map,
        }
    }
}

/// Convert a `T` into `serde_json::Value` which is an enum that can represent
/// any valid JSON data.
///
/// This conversion can fail if `T`'s implementation of `Serialize` decides to
/// fail, or if `T` contains a map with non-string keys.
///
/// ```rust
/// # use serde_json::Value;
/// let val = serde_json::to_value("s").unwrap();
/// assert_eq!(val, Value::String("s".to_owned()));
/// ```
#[cfg_attr(feature = "cargo-clippy", allow(needless_pass_by_value))]
// 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: ser::Serialize,
{
    value.serialize(Serializer)
}

/// Interpret a `serde_json::Value` as an instance of type `T`.
///
/// 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: de::Deserialize,
{
    de::Deserialize::deserialize(value)
}

/// Representation of any serializable data as a `serde_json::Value`.
pub trait ToJson {
    /// Represent `self` as a `serde_json::Value`. Note that `Value` is not a
    /// JSON string. If you need a string, use `serde_json::to_string` instead.
    ///
    /// This conversion can fail if `T`'s implementation of `Serialize` decides
    /// to fail, or if `T` contains a map with non-string keys.
    fn to_json(&self) -> Result<Value, Error>;
}

impl<T: ?Sized> ToJson for T
    where T: ser::Serialize,
{
    fn to_json(&self) -> Result<Value, Error> {
        to_value(self)
    }
}