Trait serde::de::MapAccess

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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> { ... }
}
Expand description

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

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

Required methods

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.

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

source

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.

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.

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.

source

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.

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

Implementations on Foreign Types

source

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>, 

source

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

Implementors