Trait MapAccess

pub trait MapAccess<'de> {
    type Error: Error;

    // Required methods
    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>;

    // 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> { ... }
    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.

Required 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.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementations on Foreign Types

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

where A: MapAccess<'de> + ?Sized,

type Error = <A as MapAccess<'de>>::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