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use crate::{Mapping, Value};
use std::fmt;
use std::ops;
/// A type that can be used to index into a `serde_yaml::Value`. See the `get`
/// and `get_mut` methods of `Value`.
///
/// This trait is sealed and cannot be implemented for types outside of
/// `serde_yaml`.
pub trait Index: private::Sealed {
/// Return None if the key is not already in the sequence 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 sequence or object.
#[doc(hidden)]
fn index_into_mut<'v>(&self, v: &'v mut Value) -> Option<&'v mut Value>;
/// Panic if sequence 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::Sequence(vec) => vec.get(*self),
Value::Mapping(vec) => vec.get(&Value::Number((*self).into())),
_ => None,
}
}
fn index_into_mut<'v>(&self, v: &'v mut Value) -> Option<&'v mut Value> {
match v {
Value::Sequence(vec) => vec.get_mut(*self),
Value::Mapping(vec) => vec.get_mut(&Value::Number((*self).into())),
_ => None,
}
}
fn index_or_insert<'v>(&self, v: &'v mut Value) -> &'v mut Value {
match v {
Value::Sequence(vec) => {
let len = vec.len();
vec.get_mut(*self).unwrap_or_else(|| {
panic!(
"cannot access index {} of YAML sequence of length {}",
self, len
)
})
}
Value::Mapping(map) => {
let n = Value::Number((*self).into());
// TODO: use entry() once LinkedHashMap supports entry()
if !map.contains_key(&n) {
map.insert(n.clone(), Value::Null);
}
map.get_mut(&n).unwrap()
}
_ => panic!("cannot access index {} of YAML {}", self, Type(v)),
}
}
}
impl Index for Value {
fn index_into<'v>(&self, v: &'v Value) -> Option<&'v Value> {
match v {
Value::Mapping(map) => map.get(self),
_ => None,
}
}
fn index_into_mut<'v>(&self, v: &'v mut Value) -> Option<&'v mut Value> {
match v {
Value::Mapping(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 = Mapping::new();
map.insert(self.clone(), Value::Null);
*v = Value::Mapping(map);
}
match v {
Value::Mapping(map) => {
// TODO: use entry() once LinkedHashMap supports entry()
if !map.contains_key(self) {
map.insert(self.clone(), Value::Null);
}
map.get_mut(self).unwrap()
}
_ => panic!("cannot access key {:?} in YAML {}", self, Type(v)),
}
}
}
impl Index for str {
fn index_into<'v>(&self, v: &'v Value) -> Option<&'v Value> {
Value::String(self.into()).index_into(v)
}
fn index_into_mut<'v>(&self, v: &'v mut Value) -> Option<&'v mut Value> {
Value::String(self.into()).index_into_mut(v)
}
fn index_or_insert<'v>(&self, v: &'v mut Value) -> &'v mut Value {
Value::String(self.into()).index_or_insert(v)
}
}
impl Index for String {
fn index_into<'v>(&self, v: &'v Value) -> Option<&'v Value> {
Value::String(self.clone()).index_into(v)
}
fn index_into_mut<'v>(&self, v: &'v mut Value) -> Option<&'v mut Value> {
Value::String(self.clone()).index_into_mut(v)
}
fn index_or_insert<'v>(&self, v: &'v mut Value) -> &'v mut Value {
Value::String(self.clone()).index_or_insert(v)
}
}
impl<'a, T> Index for &'a T
where
T: ?Sized + 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 Sealed for super::Value {}
impl<'a, T> Sealed for &'a T where T: ?Sized + 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::Sequence(_) => formatter.write_str("sequence"),
Value::Mapping(_) => formatter.write_str("mapping"),
}
}
}
// 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 YAML 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_sequence()` and working with the Vec directly, or matching on
// `Value::Sequence` 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_sequence`, 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_yaml::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 a sequence
/// 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 sequence.
///
/// For retrieving deeply nested values, you should have a look at the
/// `Value::pointer` method.
///
/// # Examples
///
/// ```
/// # fn yaml(i: &str) -> serde_yaml::Value { serde_yaml::from_str(i).unwrap() }
/// #
/// let data = yaml(r#"{ x: { y: [z, zz] } }"#);
///
/// assert_eq!(data["x"]["y"], yaml(r#"["z", "zz"]"#));
/// assert_eq!(data["x"]["y"][0], yaml(r#""z""#));
///
/// assert_eq!(data["a"], yaml(r#"null"#)); // returns null for undefined values
/// assert_eq!(data["a"]["b"], yaml(r#"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_yaml::Value` using the syntax `value[0] = ...` or
/// `value["k"] = ...`.
///
/// If the index is a number, the value must be a sequence of length bigger
/// than the index. Indexing into a value that is not a sequence or a
/// sequence 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
///
/// ```
/// # fn yaml(i: &str) -> serde_yaml::Value { serde_yaml::from_str(i).unwrap() }
/// #
/// let mut data = yaml(r#"{x: 0}"#);
///
/// // replace an existing key
/// data["x"] = yaml(r#"1"#);
///
/// // insert a new key
/// data["y"] = yaml(r#"[false, false, false]"#);
///
/// // replace a value in a sequence
/// data["y"][0] = yaml(r#"true"#);
///
/// // inserted a deeply nested key
/// data["a"]["b"]["c"]["d"] = yaml(r#"true"#);
///
/// println!("{:?}", data);
/// ```
fn index_mut(&mut self, index: I) -> &mut Value {
index.index_or_insert(self)
}
}