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Add helper CowStrVisitor and CowBytesVisitor types
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‎serde/src/de/value.rs‎

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@@ -1727,6 +1727,292 @@ where
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////////////////////////////////////////////////////////////////////////////////
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/// A visitor and a seed which is able to return borrowed `Cow<str>`.
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///
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/// Serde implementation is generic for any `Cow<T>` and because visitor has no
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/// hint methods for arbitrary borrowing types, [`Cow`] is always deserialized as
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/// [`Cow::Owned`] variant. This visitor and seed allows to deserialize borrowed
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/// variant of a [`Cow`] for a string.
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///
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/// This is useful when you want to read `Cow` from a [`MapAccess`] or a [`SeqAccess`].
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///
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/// # Example
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///
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/// This example implements a simple XML DOM node:
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/// ```
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/// # use serde::de::{DeserializeSeed, Deserializer, MapAccess, Visitor};
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/// # use serde::de::value::CowStrVisitor;
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/// # use std::borrow::Cow;
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/// #
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/// struct Element<'a> {
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/// name: Cow<'a, str>,
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/// children: Vec<Node<'a>>,
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/// }
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/// enum Node<'a> {
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/// Text(Cow<'a, str>),
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/// Element(Element<'a>),
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/// }
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///
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/// impl<'de> Visitor<'de> for Element<'de> {
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/// type Value = Self;
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///
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/// fn expecting(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
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/// f.write_str("a map")
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/// }
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///
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/// fn visit_map<A>(mut self, mut map: A) -> Result<Self::Value, A::Error>
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/// where
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/// A: MapAccess<'de>,
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/// {
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/// while let Some(key) = map.next_key_seed(CowStrVisitor)? {
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/// if "$text" == key {
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/// let text = map.next_value_seed(CowStrVisitor)?;
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/// self.children.push(Node::Text(text));
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/// } else {
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/// let elem = Element { name: key, children: Vec::new() };
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/// let elem = map.next_value_seed(elem)?;
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/// self.children.push(Node::Element(elem));
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/// }
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/// }
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/// Ok(self)
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/// }
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/// }
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///
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/// impl<'de> DeserializeSeed<'de> for Element<'de> {
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/// type Value = Self;
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///
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/// fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
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/// where
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/// D: Deserializer<'de>,
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/// {
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/// deserializer.deserialize_map(self)
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/// }
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/// }
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/// ```
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///
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/// [`MapAccess`]: crate::de::MapAccess
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#[cfg(any(feature = "std", feature = "alloc"))]
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#[doc(alias = "CowStrSeed")]
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#[derive(Debug, Copy, Clone)]
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pub struct CowStrVisitor;
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#[cfg(any(feature = "std", feature = "alloc"))]
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impl<'de> Visitor<'de> for CowStrVisitor {
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type Value = Cow<'de, str>;
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fn expecting(&self, f: &mut fmt::Formatter) -> fmt::Result {
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f.write_str("a string")
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}
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fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
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where
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E: de::Error,
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{
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Ok(Cow::Owned(v.to_owned()))
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}
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#[inline]
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fn visit_borrowed_str<E>(self, v: &'de str) -> Result<Self::Value, E>
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where
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E: de::Error,
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{
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Ok(Cow::Borrowed(v))
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}
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#[inline]
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fn visit_string<E>(self, v: String) -> Result<Self::Value, E>
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where
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E: de::Error,
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{
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Ok(Cow::Owned(v))
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}
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fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>
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where
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E: de::Error,
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{
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match str::from_utf8(v) {
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Ok(s) => Ok(Cow::Owned(s.to_owned())),
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Err(_) => Err(de::Error::invalid_value(de::Unexpected::Bytes(v), &self)),
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}
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}
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fn visit_borrowed_bytes<E>(self, v: &'de [u8]) -> Result<Self::Value, E>
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where
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E: de::Error,
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{
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match str::from_utf8(v) {
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Ok(s) => Ok(Cow::Borrowed(s)),
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Err(_) => Err(de::Error::invalid_value(de::Unexpected::Bytes(v), &self)),
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}
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}
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fn visit_byte_buf<E>(self, v: Vec<u8>) -> Result<Self::Value, E>
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where
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E: de::Error,
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{
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match String::from_utf8(v) {
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Ok(s) => Ok(Cow::Owned(s)),
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Err(e) => Err(de::Error::invalid_value(
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de::Unexpected::Bytes(&e.into_bytes()),
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&self,
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)),
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}
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}
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}
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#[cfg(any(feature = "std", feature = "alloc"))]
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impl<'de> de::DeserializeSeed<'de> for CowStrVisitor {
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type Value = Cow<'de, str>;
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fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
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where
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D: Deserializer<'de>,
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{
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deserializer.deserialize_string(self)
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}
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}
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////////////////////////////////////////////////////////////////////////////////
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/// A visitor and a seed which is able to return borrowed `Cow<[u8]>`.
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///
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/// Serde implementation is generic for any `Cow<T>` and because visitor has no
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/// hint methods for arbitrary borrowing types, [`Cow`] is always deserialized as
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/// [`Cow::Owned`] variant. This visitor and seed allows to deserialize borrowed
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/// variant of a [`Cow`] for a byte slice.
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///
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/// This is useful when you want to read `Cow` from a [`MapAccess`] or a [`SeqAccess`].
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///
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/// # Example
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///
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/// This example implements a simple XML DOM node:
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/// ```
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/// # use serde::de::{DeserializeSeed, Deserializer, MapAccess, Visitor};
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/// # use serde::de::value::CowBytesVisitor;
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/// # use std::borrow::Cow;
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/// #
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/// struct Element<'a> {
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/// name: Cow<'a, [u8]>,
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/// children: Vec<Node<'a>>,
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/// }
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/// enum Node<'a> {
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/// Text(Cow<'a, [u8]>),
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/// Element(Element<'a>),
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/// }
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///
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/// impl<'de> Visitor<'de> for Element<'de> {
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/// type Value = Self;
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///
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/// fn expecting(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
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/// f.write_str("a map")
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/// }
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///
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/// fn visit_map<A>(mut self, mut map: A) -> Result<Self::Value, A::Error>
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/// where
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/// A: MapAccess<'de>,
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/// {
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/// while let Some(key) = map.next_key_seed(CowBytesVisitor)? {
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/// if *b"$text" == *key {
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/// let text = map.next_value_seed(CowBytesVisitor)?;
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/// self.children.push(Node::Text(text));
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/// } else {
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/// let elem = Element { name: key, children: Vec::new() };
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/// let elem = map.next_value_seed(elem)?;
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/// self.children.push(Node::Element(elem));
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/// }
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/// }
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/// Ok(self)
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/// }
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/// }
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///
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/// impl<'de> DeserializeSeed<'de> for Element<'de> {
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/// type Value = Self;
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///
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/// fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
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/// where
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/// D: Deserializer<'de>,
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/// {
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/// deserializer.deserialize_map(self)
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/// }
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/// }
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/// ```
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///
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/// [`MapAccess`]: crate::de::MapAccess
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#[cfg(any(feature = "std", feature = "alloc"))]
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#[doc(alias = "CowBytesSeed")]
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#[derive(Debug, Copy, Clone)]
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pub struct CowBytesVisitor;
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#[cfg(any(feature = "std", feature = "alloc"))]
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impl<'de> Visitor<'de> for CowBytesVisitor {
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type Value = Cow<'de, [u8]>;
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fn expecting(&self, f: &mut fmt::Formatter) -> fmt::Result {
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f.write_str("a byte array")
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}
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fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
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where
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E: de::Error,
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{
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Ok(Cow::Owned(v.as_bytes().to_owned()))
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}
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#[inline]
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fn visit_borrowed_str<E>(self, v: &'de str) -> Result<Self::Value, E>
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where
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E: de::Error,
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{
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Ok(Cow::Borrowed(v.as_bytes()))
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}
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#[inline]
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fn visit_string<E>(self, v: String) -> Result<Self::Value, E>
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where
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E: de::Error,
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{
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Ok(Cow::Owned(v.into_bytes()))
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}
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fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>
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where
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E: de::Error,
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{
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Ok(Cow::Owned(v.to_owned()))
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}
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#[inline]
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fn visit_borrowed_bytes<E>(self, v: &'de [u8]) -> Result<Self::Value, E>
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where
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E: de::Error,
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{
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Ok(Cow::Borrowed(v))
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}
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#[inline]
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fn visit_byte_buf<E>(self, v: Vec<u8>) -> Result<Self::Value, E>
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where
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E: de::Error,
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{
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Ok(Cow::Owned(v))
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}
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}
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#[cfg(any(feature = "std", feature = "alloc"))]
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impl<'de> de::DeserializeSeed<'de> for CowBytesVisitor {
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type Value = Cow<'de, [u8]>;
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fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
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where
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D: Deserializer<'de>,
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{
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deserializer.deserialize_byte_buf(self)
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}
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}
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////////////////////////////////////////////////////////////////////////////////
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mod private {
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use crate::lib::*;
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