Trait serde::ser::SerializeMap

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pub trait SerializeMap {
    type Ok;
    type Error: Error;

    // Required methods
    fn serialize_key<T>(&mut self, key: &T) -> Result<(), Self::Error>
       where T: Serialize + ?Sized;
    fn serialize_value<T>(&mut self, value: &T) -> Result<(), Self::Error>
       where T: Serialize + ?Sized;
    fn end(self) -> Result<Self::Ok, Self::Error>;

    // Provided method
    fn serialize_entry<K, V>(
        &mut self,
        key: &K,
        value: &V
    ) -> Result<(), Self::Error>
       where K: Serialize + ?Sized,
             V: Serialize + ?Sized { ... }
}

Expand description

Returned from Serializer::serialize_map.

Example use

use serde::ser::{Serialize, SerializeMap, Serializer};

impl<K, V> Serialize for HashMap<K, V>
where
    K: Serialize,
    V: Serialize,
{
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        let mut map = serializer.serialize_map(Some(self.len()))?;
        for (k, v) in self {
            map.serialize_entry(k, v)?;
        }
        map.end()
    }
}

Example implementation

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

Required Associated Types§

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type Ok

Must match the Ok type of our Serializer.

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type Error: Error

Must match the Error type of our Serializer.

Required Methods§

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fn serialize_key<T>(&mut self, key: &T) -> Result<(), Self::Error>where T: Serialize + ?Sized,

Serialize a map key.

If possible, Serialize implementations are encouraged to use serialize_entry instead as it may be implemented more efficiently in some formats compared to a pair of calls to serialize_key and serialize_value.

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fn serialize_value<T>(&mut self, value: &T) -> Result<(), Self::Error>where T: Serialize + ?Sized,

Serialize a map value.

Panics

Calling serialize_value before serialize_key is incorrect and is allowed to panic or produce bogus results.

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fn end(self) -> Result<Self::Ok, Self::Error>

Finish serializing a map.

Provided Methods§

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fn serialize_entry<K, V>( &mut self, key: &K, value: &V ) -> Result<(), Self::Error>where K: Serialize + ?Sized, V: Serialize + ?Sized,

Serialize a map entry consisting of a key and a value.

Some Serialize types are not able to hold a key and value in memory at the same time so SerializeMap implementations are required to support serialize_key and serialize_value individually. The serialize_entry method allows serializers to optimize for the case where key and value are both available. Serialize implementations are encouraged to use serialize_entry if possible.

The default implementation delegates to serialize_key and serialize_value. This is appropriate for serializers that do not care about performance or are not able to optimize serialize_entry any better than this.