[][src]Struct serde::de::IgnoredAny

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.

This code runs with edition 2018
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)
    }
}

// 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<'de> Deserialize<'de> for IgnoredAny[src]

impl<'de> Visitor<'de> for IgnoredAny[src]

type Value = IgnoredAny

The value produced by this visitor.

fn visit_i8<E>(self, v: i8) -> Result<Self::Value, E> where
    E: Error
[src]

The input contains an i8. Read more

fn visit_i16<E>(self, v: i16) -> Result<Self::Value, E> where
    E: Error
[src]

The input contains an i16. Read more

fn visit_i32<E>(self, v: i32) -> Result<Self::Value, E> where
    E: Error
[src]

The input contains an i32. Read more

fn visit_i128<E>(self, v: i128) -> Result<Self::Value, E> where
    E: Error
[src]

The input contains a i128. Read more

fn visit_u8<E>(self, v: u8) -> Result<Self::Value, E> where
    E: Error
[src]

The input contains a u8. Read more

fn visit_u16<E>(self, v: u16) -> Result<Self::Value, E> where
    E: Error
[src]

The input contains a u16. Read more

fn visit_u32<E>(self, v: u32) -> Result<Self::Value, E> where
    E: Error
[src]

The input contains a u32. Read more

fn visit_u128<E>(self, v: u128) -> Result<Self::Value, E> where
    E: Error
[src]

The input contains a u128. Read more

fn visit_f32<E>(self, v: f32) -> Result<Self::Value, E> where
    E: Error
[src]

The input contains an f32. Read more

fn visit_char<E>(self, v: char) -> Result<Self::Value, E> where
    E: Error
[src]

The input contains a char. Read more

fn visit_borrowed_str<E>(self, v: &'de str) -> Result<Self::Value, E> where
    E: Error
[src]

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
[src]

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
[src]

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
[src]

The input contains a byte array and ownership of the byte array is being given to the Visitor. Read more

impl Default for IgnoredAny[src]

impl Clone for IgnoredAny[src]

fn clone_from(&mut self, source: &Self)1.0.0[src]

Performs copy-assignment from source. Read more

impl Copy for IgnoredAny[src]

impl Debug for IgnoredAny[src]

Auto Trait Implementations

impl Send for IgnoredAny

impl Unpin for IgnoredAny

impl Sync for IgnoredAny

impl UnwindSafe for IgnoredAny

impl RefUnwindSafe for IgnoredAny

Blanket Implementations

impl<'de, T> Expected for T where
    T: Visitor<'de>, 
[src]

impl<T> DeserializeOwned for T where
    T: Deserialize<'de>, 
[src]

impl<T> From<T> for T[src]

impl<T, U> Into<U> for T where
    U: From<T>, 
[src]

impl<T> ToOwned for T where
    T: Clone
[src]

type Owned = T

The resulting type after obtaining ownership.

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 
[src]

type Error = Infallible

The type returned in the event of a conversion error.

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 
[src]

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

impl<T> Borrow<T> for T where
    T: ?Sized
[src]

impl<T> BorrowMut<T> for T where
    T: ?Sized
[src]

impl<T> Any for T where
    T: 'static + ?Sized
[src]