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

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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Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

impl Debug for IgnoredAny
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Formats the value using the given formatter.

impl Default for IgnoredAny
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Returns the "default value" for a type. Read more

impl<'de> Visitor<'de> for IgnoredAny
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The value produced by this visitor.

Format a message stating what data this Visitor expects to receive. Read more

The input contains a boolean. Read more

The input contains an i32. Read more

The input contains a u64. Read more

The input contains an f64. Read more

The input contains a string. The lifetime of the string is ephemeral and it may be destroyed after this method returns. Read more

The input contains an optional that is absent. Read more

The input contains an optional that is present. Read more

The input contains a newtype struct. Read more

The input contains a unit (). Read more

The input contains a sequence of elements. Read more

The input contains a key-value map. Read more

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

The input contains an i8. Read more

The input contains an i16. Read more

The input contains an i32. Read more

The input contains a u8. Read more

The input contains a u16. Read more

The input contains a u32. Read more

The input contains an f32. Read more

The input contains a char. Read more

The input contains a string that lives at least as long as the Deserializer. Read more

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

The input contains a byte array that lives at least as long as the Deserializer. Read more

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

The input contains an enum. Read more

impl<'de> Deserialize<'de> for IgnoredAny
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Deserialize this value from the given Serde deserializer. Read more