Struct serde::de::IgnoredAny

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pub struct IgnoredAny;
Expand description

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)
    }
}

// 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§

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impl Clone for IgnoredAny

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fn clone(&self) -> IgnoredAny

Returns a copy of the value. Read more
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fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
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impl Debug for IgnoredAny

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fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
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impl Default for IgnoredAny

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fn default() -> IgnoredAny

Returns the “default value” for a type. Read more
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impl<'de> Deserialize<'de> for IgnoredAny

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fn deserialize<D>(deserializer: D) -> Result<IgnoredAny, D::Error>
where D: Deserializer<'de>,

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

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type Value = IgnoredAny

The value produced by this visitor.
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fn expecting(&self, formatter: &mut Formatter<'_>) -> Result

Format a message stating what data this Visitor expects to receive. Read more
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fn visit_bool<E>(self, x: bool) -> Result<Self::Value, E>

The input contains a boolean. Read more
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fn visit_i64<E>(self, x: i64) -> Result<Self::Value, E>

The input contains an i64. Read more
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fn visit_i128<E>(self, x: i128) -> Result<Self::Value, E>

The input contains a i128. Read more
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fn visit_u64<E>(self, x: u64) -> Result<Self::Value, E>

The input contains a u64. Read more
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fn visit_u128<E>(self, x: u128) -> Result<Self::Value, E>

The input contains a u128. Read more
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fn visit_f64<E>(self, x: f64) -> Result<Self::Value, E>

The input contains an f64. Read more
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fn visit_str<E>(self, s: &str) -> Result<Self::Value, E>
where 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
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fn visit_none<E>(self) -> Result<Self::Value, E>

The input contains an optional that is absent. Read more
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fn visit_some<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
where D: Deserializer<'de>,

The input contains an optional that is present. Read more
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fn visit_newtype_struct<D>( self, deserializer: D ) -> Result<Self::Value, D::Error>
where D: Deserializer<'de>,

The input contains a newtype struct. Read more
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fn visit_unit<E>(self) -> Result<Self::Value, E>

The input contains a unit (). Read more
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fn visit_seq<A>(self, seq: A) -> Result<Self::Value, A::Error>
where A: SeqAccess<'de>,

The input contains a sequence of elements. Read more
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fn visit_map<A>(self, map: A) -> Result<Self::Value, A::Error>
where A: MapAccess<'de>,

The input contains a key-value map. Read more
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fn visit_bytes<E>(self, bytes: &[u8]) -> Result<Self::Value, E>
where 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
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fn visit_enum<A>(self, data: A) -> Result<Self::Value, A::Error>
where A: EnumAccess<'de>,

The input contains an enum. Read more
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fn visit_i8<E>(self, v: i8) -> Result<Self::Value, E>
where E: Error,

The input contains an i8. Read more
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fn visit_i16<E>(self, v: i16) -> Result<Self::Value, E>
where E: Error,

The input contains an i16. Read more
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fn visit_i32<E>(self, v: i32) -> Result<Self::Value, E>
where E: Error,

The input contains an i32. Read more
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fn visit_u8<E>(self, v: u8) -> Result<Self::Value, E>
where E: Error,

The input contains a u8. Read more
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fn visit_u16<E>(self, v: u16) -> Result<Self::Value, E>
where E: Error,

The input contains a u16. Read more
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fn visit_u32<E>(self, v: u32) -> Result<Self::Value, E>
where E: Error,

The input contains a u32. Read more
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fn visit_f32<E>(self, v: f32) -> Result<Self::Value, E>
where E: Error,

The input contains an f32. Read more
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fn visit_char<E>(self, v: char) -> Result<Self::Value, E>
where E: Error,

The input contains a char. Read more
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fn visit_borrowed_str<E>(self, v: &'de str) -> Result<Self::Value, E>
where E: Error,

The input contains a string that lives at least as long as the Deserializer. Read more
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fn visit_string<E>(self, v: String) -> Result<Self::Value, E>
where E: Error,

The input contains a string and ownership of the string is being given to the Visitor. Read more
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fn visit_borrowed_bytes<E>(self, v: &'de [u8]) -> Result<Self::Value, E>
where E: Error,

The input contains a byte array that lives at least as long as the Deserializer. Read more
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fn visit_byte_buf<E>(self, v: Vec<u8>) -> Result<Self::Value, E>
where E: Error,

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

Auto Trait Implementations§

Blanket Implementations§

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<'de, T> Expected for T
where T: Visitor<'de>,

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fn fmt(&self, formatter: &mut Formatter<'_>) -> Result<(), Error>

Format an explanation of what data was being expected. Same signature as the Display and Debug traits.
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T> ToOwned for T
where T: Clone,

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type Owned = T

The resulting type after obtaining ownership.
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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
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impl<T> DeserializeOwned for T
where T: for<'de> Deserialize<'de>,