Struct serde::de::IgnoredAny
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pub struct IgnoredAny;
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.
use std::fmt; use std::marker::PhantomData; use serde::de::{self, Deserialize, DeserializeSeed, Deserializer, Visitor, SeqAccess, IgnoredAny}; /// 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: /// /// ```rust /// 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) } } // 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)?;
Trait Implementations
impl Copy for IgnoredAny
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impl Clone for IgnoredAny
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fn clone(&self) -> IgnoredAny
Returns a copy of the value. Read more
fn clone_from(&mut self, source: &Self)
1.0.0
Performs copy-assignment from source
. Read more
impl Debug for IgnoredAny
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impl Default for IgnoredAny
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fn default() -> IgnoredAny
Returns the "default value" for a type. Read more
impl<'de> Visitor<'de> for IgnoredAny
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type Value = IgnoredAny
The value produced by this visitor.
fn expecting(&self, formatter: &mut Formatter) -> Result
Format a message stating what data this Visitor expects to receive. Read more
fn visit_bool<E>(self, x: bool) -> Result<Self::Value, E>
The input contains a boolean. Read more
fn visit_i64<E>(self, x: i64) -> Result<Self::Value, E>
The input contains an i32
. Read more
fn visit_u64<E>(self, x: u64) -> Result<Self::Value, E>
The input contains a u64
. Read more
fn visit_f64<E>(self, x: f64) -> Result<Self::Value, E>
The input contains an f64
. Read more
fn visit_str<E>(self, s: &str) -> Result<Self::Value, E> where
E: Error,
E: Error,
The input contains a string. The lifetime of the string is ephemeral and it may be destroyed after this method returns. Read more
fn visit_none<E>(self) -> Result<Self::Value, E>
The input contains an optional that is absent. Read more
fn visit_some<D>(self, deserializer: D) -> Result<Self::Value, D::Error> where
D: Deserializer<'de>,
D: Deserializer<'de>,
The input contains an optional that is present. Read more
fn visit_newtype_struct<D>(
self,
deserializer: D
) -> Result<Self::Value, D::Error> where
D: Deserializer<'de>,
self,
deserializer: D
) -> Result<Self::Value, D::Error> where
D: Deserializer<'de>,
The input contains a newtype struct. Read more
fn visit_unit<E>(self) -> Result<Self::Value, E>
The input contains a unit ()
. Read more
fn visit_seq<A>(self, seq: A) -> Result<Self::Value, A::Error> where
A: SeqAccess<'de>,
A: SeqAccess<'de>,
The input contains a sequence of elements. Read more
fn visit_map<A>(self, map: A) -> Result<Self::Value, A::Error> where
A: MapAccess<'de>,
A: MapAccess<'de>,
The input contains a key-value map. Read more
fn visit_bytes<E>(self, bytes: &[u8]) -> Result<Self::Value, E> where
E: Error,
E: Error,
The input contains a byte array. The lifetime of the byte array is ephemeral and it may be destroyed after this method returns. Read more
fn visit_i8<E>(self, v: i8) -> Result<Self::Value, E> where
E: Error,
E: Error,
The input contains an i8
. Read more
fn visit_i16<E>(self, v: i16) -> Result<Self::Value, E> where
E: Error,
E: Error,
The input contains an i16
. Read more
fn visit_i32<E>(self, v: i32) -> Result<Self::Value, E> where
E: Error,
E: Error,
The input contains an i32
. Read more
fn visit_u8<E>(self, v: u8) -> Result<Self::Value, E> where
E: Error,
E: Error,
The input contains a u8
. Read more
fn visit_u16<E>(self, v: u16) -> Result<Self::Value, E> where
E: Error,
E: Error,
The input contains a u16
. Read more
fn visit_u32<E>(self, v: u32) -> Result<Self::Value, E> where
E: Error,
E: Error,
The input contains a u32
. Read more
fn visit_f32<E>(self, v: f32) -> Result<Self::Value, E> where
E: Error,
E: Error,
The input contains an f32
. Read more
fn visit_char<E>(self, v: char) -> Result<Self::Value, E> where
E: Error,
E: Error,
The input contains a char
. Read more
fn visit_borrowed_str<E>(self, v: &'de str) -> Result<Self::Value, E> where
E: Error,
E: Error,
The input contains a string that lives at least as long as the Deserializer
. Read more
fn visit_string<E>(self, v: String) -> Result<Self::Value, E> where
E: Error,
E: Error,
The input contains a string and ownership of the string is being given to the Visitor
. Read more
fn visit_borrowed_bytes<E>(self, v: &'de [u8]) -> Result<Self::Value, E> where
E: Error,
E: Error,
The input contains a byte array that lives at least as long as the Deserializer
. Read more
fn visit_byte_buf<E>(self, v: Vec<u8>) -> Result<Self::Value, E> where
E: Error,
E: Error,
The input contains a byte array and ownership of the byte array is being given to the Visitor
. Read more
fn visit_enum<A>(self, data: A) -> Result<Self::Value, A::Error> where
A: EnumAccess<'de>,
A: EnumAccess<'de>,
The input contains an enum. Read more
impl<'de> Deserialize<'de> for IgnoredAny
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fn deserialize<D>(deserializer: D) -> Result<IgnoredAny, D::Error> where
D: Deserializer<'de>,
D: Deserializer<'de>,
Deserialize this value from the given Serde deserializer. Read more