Trait serde::de::MapAccess

pub trait MapAccess<'de> {
    type Error: Error;
    fn next_key_seed<K>(
        &mut self, 
        seed: K
    ) -> Result<Option<K::Value>, Self::Error>
    where
        K: DeserializeSeed<'de>;
    fn next_value_seed<V>(&mut self, seed: V) -> Result<V::Value, Self::Error>
    where
        V: DeserializeSeed<'de>;

    fn next_entry_seed<K, V>(
        &mut self, 
        kseed: K, 
        vseed: V
    ) -> Result<Option<(K::Value, V::Value)>, Self::Error>
    where
        K: DeserializeSeed<'de>,
        V: DeserializeSeed<'de>,
    { ... }
    fn next_key<K>(&mut self) -> Result<Option<K>, Self::Error>
    where
        K: Deserialize<'de>,
    { ... }
    fn next_value<V>(&mut self) -> Result<V, Self::Error>
    where
        V: Deserialize<'de>,
    { ... }
    fn next_entry<K, V>(&mut self) -> Result<Option<(K, V)>, Self::Error>
    where
        K: Deserialize<'de>,
        V: Deserialize<'de>,
    { ... }
    fn size_hint(&self) -> Option<usize> { ... }
}

Provides a Visitor access to each entry of a map in the input.

This is a trait that a Deserializer passes to a Visitor implementation.

Lifetime

The 'de lifetime of this trait is the lifetime of data that may be borrowed by deserialized map entries. See the page Understanding deserializer lifetimes for a more detailed explanation of these lifetimes.

Example implementation

The example data format presented on the website demonstrates an implementation of MapAccess for a basic JSON data format.

Associated Types

type Error: Error

The error type that can be returned if some error occurs during deserialization.

Required Methods

fn next_key_seed<K>(&mut self, seed: K) -> Result<Option<K::Value>, Self::Error> where
    K: DeserializeSeed<'de>, 

This returns Ok(Some(key)) for the next key in the map, or Ok(None) if there are no more remaining entries.

Deserialize implementations should typically use MapAccess::next_key or MapAccess::next_entry instead.

fn next_value_seed<V>(&mut self, seed: V) -> Result<V::Value, Self::Error> where
    V: DeserializeSeed<'de>, 

This returns a Ok(value) for the next value in the map.

Deserialize implementations should typically use MapAccess::next_value instead.

Panics

Calling next_value_seed before next_key_seed is incorrect and is allowed to panic or return bogus results.

Provided Methods

fn next_entry_seed<K, V>(
    &mut self,
    kseed: K,
    vseed: V
) -> Result<Option<(K::Value, V::Value)>, Self::Error> where
    K: DeserializeSeed<'de>,
    V: DeserializeSeed<'de>, 

This returns Ok(Some((key, value))) for the next (key-value) pair in the map, or Ok(None) if there are no more remaining items.

MapAccess implementations should override the default behavior if a more efficient implementation is possible.

Deserialize implementations should typically use MapAccess::next_entry instead.

fn next_key<K>(&mut self) -> Result<Option<K>, Self::Error> where
    K: Deserialize<'de>, 

This returns Ok(Some(key)) for the next key in the map, or Ok(None) if there are no more remaining entries.

This method exists as a convenience for Deserialize implementations. MapAccess implementations should not override the default behavior.

fn next_value<V>(&mut self) -> Result<V, Self::Error> where
    V: Deserialize<'de>, 

This returns a Ok(value) for the next value in the map.

This method exists as a convenience for Deserialize implementations. MapAccess implementations should not override the default behavior.

Panics

Calling next_value before next_key is incorrect and is allowed to panic or return bogus results.

fn next_entry<K, V>(&mut self) -> Result<Option<(K, V)>, Self::Error> where
    K: Deserialize<'de>,
    V: Deserialize<'de>, 

This returns Ok(Some((key, value))) for the next (key-value) pair in the map, or Ok(None) if there are no more remaining items.

This method exists as a convenience for Deserialize implementations. MapAccess implementations should not override the default behavior.

fn size_hint(&self) -> Option<usize>

Returns the number of entries remaining in the map, if known.

Implementations on Foreign Types

impl<'de, 'a, A> MapAccess<'de> for &'a mut A where
    A: MapAccess<'de>, 

type Error = A::Error

fn next_key_seed<K>(&mut self, seed: K) -> Result<Option<K::Value>, Self::Error> where
    K: DeserializeSeed<'de>, 

fn next_value_seed<V>(&mut self, seed: V) -> Result<V::Value, Self::Error> where
    V: DeserializeSeed<'de>, 

fn next_entry_seed<K, V>(
    &mut self,
    kseed: K,
    vseed: V
) -> Result<Option<(K::Value, V::Value)>, Self::Error> where
    K: DeserializeSeed<'de>,
    V: DeserializeSeed<'de>, 

fn next_entry<K, V>(&mut self) -> Result<Option<(K, V)>, Self::Error> where
    K: Deserialize<'de>,
    V: Deserialize<'de>, 

fn next_key<K>(&mut self) -> Result<Option<K>, Self::Error> where
    K: Deserialize<'de>, 

fn next_value<V>(&mut self) -> Result<V, Self::Error> where
    V: Deserialize<'de>, 

fn size_hint(&self) -> Option<usize>

Implementors

• impl<'de, I, E> MapAccess<'de> for MapDeserializer<'de, I, E> where
    I: Iterator,
    I::Item: Pair,
    <I::Item as Pair>::First: IntoDeserializer<'de, E>,
    <I::Item as Pair>::Second: IntoDeserializer<'de, E>,
    E: Error,  type Error = E;