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Diffstat (limited to 'src/de/ignored_any.rs')
| -rw-r--r-- | src/de/ignored_any.rs | 243 |
1 files changed, 243 insertions, 0 deletions
diff --git a/src/de/ignored_any.rs b/src/de/ignored_any.rs new file mode 100644 index 0000000..9ed438e --- /dev/null +++ b/src/de/ignored_any.rs @@ -0,0 +1,243 @@ +use lib::*; + +use de::{ + Deserialize, Deserializer, EnumAccess, Error, MapAccess, SeqAccess, VariantAccess, Visitor, +}; + +/// An efficient way of discarding data from a deserializer. +/// +/// Think of this like `serde_json::Value` in that it can be deserialized from +/// any type, except that it does not store any information about the data that +/// gets deserialized. +/// +/// ```edition2018 +/// use std::fmt; +/// use std::marker::PhantomData; +/// +/// use serde::de::{ +/// self, Deserialize, DeserializeSeed, Deserializer, IgnoredAny, SeqAccess, Visitor, +/// }; +/// +/// /// A seed that can be used to deserialize only the `n`th element of a sequence +/// /// while efficiently discarding elements of any type before or after index `n`. +/// /// +/// /// For example to deserialize only the element at index 3: +/// /// +/// /// ``` +/// /// NthElement::new(3).deserialize(deserializer) +/// /// ``` +/// pub struct NthElement<T> { +/// n: usize, +/// marker: PhantomData<T>, +/// } +/// +/// impl<T> NthElement<T> { +/// pub fn new(n: usize) -> Self { +/// NthElement { +/// n: n, +/// marker: PhantomData, +/// } +/// } +/// } +/// +/// impl<'de, T> Visitor<'de> for NthElement<T> +/// where +/// T: Deserialize<'de>, +/// { +/// type Value = T; +/// +/// fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result { +/// write!( +/// formatter, +/// "a sequence in which we care about element {}", +/// self.n +/// ) +/// } +/// +/// fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error> +/// where +/// A: SeqAccess<'de>, +/// { +/// // Skip over the first `n` elements. +/// for i in 0..self.n { +/// // It is an error if the sequence ends before we get to element `n`. +/// if seq.next_element::<IgnoredAny>()?.is_none() { +/// return Err(de::Error::invalid_length(i, &self)); +/// } +/// } +/// +/// // Deserialize the one we care about. +/// let nth = match seq.next_element()? { +/// Some(nth) => nth, +/// None => { +/// return Err(de::Error::invalid_length(self.n, &self)); +/// } +/// }; +/// +/// // Skip over any remaining elements in the sequence after `n`. +/// while let Some(IgnoredAny) = seq.next_element()? { +/// // ignore +/// } +/// +/// Ok(nth) +/// } +/// } +/// +/// impl<'de, T> DeserializeSeed<'de> for NthElement<T> +/// where +/// T: Deserialize<'de>, +/// { +/// type Value = T; +/// +/// fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error> +/// where +/// D: Deserializer<'de>, +/// { +/// deserializer.deserialize_seq(self) +/// } +/// } +/// +/// # fn example<'de, D>(deserializer: D) -> Result<(), D::Error> +/// # where +/// # D: Deserializer<'de>, +/// # { +/// // Deserialize only the sequence element at index 3 from this deserializer. +/// // The element at index 3 is required to be a string. Elements before and +/// // after index 3 are allowed to be of any type. +/// let s: String = NthElement::new(3).deserialize(deserializer)?; +/// # Ok(()) +/// # } +/// ``` +#[derive(Copy, Clone, Debug, Default)] +pub struct IgnoredAny; + +impl<'de> Visitor<'de> for IgnoredAny { + type Value = IgnoredAny; + + fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result { + formatter.write_str("anything at all") + } + + #[inline] + fn visit_bool<E>(self, x: bool) -> Result<Self::Value, E> { + let _ = x; + Ok(IgnoredAny) + } + + #[inline] + fn visit_i64<E>(self, x: i64) -> Result<Self::Value, E> { + let _ = x; + Ok(IgnoredAny) + } + + serde_if_integer128! { + #[inline] + fn visit_i128<E>(self, x: i128) -> Result<Self::Value, E> { + let _ = x; + Ok(IgnoredAny) + } + } + + #[inline] + fn visit_u64<E>(self, x: u64) -> Result<Self::Value, E> { + let _ = x; + Ok(IgnoredAny) + } + + serde_if_integer128! { + #[inline] + fn visit_u128<E>(self, x: u128) -> Result<Self::Value, E> { + let _ = x; + Ok(IgnoredAny) + } + } + + #[inline] + fn visit_f64<E>(self, x: f64) -> Result<Self::Value, E> { + let _ = x; + Ok(IgnoredAny) + } + + #[inline] + fn visit_str<E>(self, s: &str) -> Result<Self::Value, E> + where + E: Error, + { + let _ = s; + Ok(IgnoredAny) + } + + #[inline] + fn visit_none<E>(self) -> Result<Self::Value, E> { + Ok(IgnoredAny) + } + + #[inline] + fn visit_some<D>(self, deserializer: D) -> Result<Self::Value, D::Error> + where + D: Deserializer<'de>, + { + IgnoredAny::deserialize(deserializer) + } + + #[inline] + fn visit_newtype_struct<D>(self, deserializer: D) -> Result<Self::Value, D::Error> + where + D: Deserializer<'de>, + { + IgnoredAny::deserialize(deserializer) + } + + #[inline] + fn visit_unit<E>(self) -> Result<Self::Value, E> { + Ok(IgnoredAny) + } + + #[inline] + fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error> + where + A: SeqAccess<'de>, + { + while let Some(IgnoredAny) = try!(seq.next_element()) { + // Gobble + } + Ok(IgnoredAny) + } + + #[inline] + fn visit_map<A>(self, mut map: A) -> Result<Self::Value, A::Error> + where + A: MapAccess<'de>, + { + while let Some((IgnoredAny, IgnoredAny)) = try!(map.next_entry()) { + // Gobble + } + Ok(IgnoredAny) + } + + #[inline] + fn visit_bytes<E>(self, bytes: &[u8]) -> Result<Self::Value, E> + where + E: Error, + { + let _ = bytes; + Ok(IgnoredAny) + } + + fn visit_enum<A>(self, data: A) -> Result<Self::Value, A::Error> + where + A: EnumAccess<'de>, + { + try!(data.variant::<IgnoredAny>()).1.newtype_variant() + } +} + +impl<'de> Deserialize<'de> for IgnoredAny { + #[inline] + fn deserialize<D>(deserializer: D) -> Result<IgnoredAny, D::Error> + where + D: Deserializer<'de>, + { + deserializer.deserialize_ignored_any(IgnoredAny) + } +} |