[][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.

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(())
# }

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.

impl Default for IgnoredAny[src]

impl Clone for IgnoredAny[src]

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> ToOwned for T where
    T: Clone
[src]

type Owned = T

The resulting type after obtaining ownership.

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

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

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

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

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