Trait serde::Serializer [−] [src]

pub trait Serializer: Sized {
    type Ok;
    type Error: Error;
    type SerializeSeq: SerializeSeq<Ok = Self::Ok, Error = Self::Error>;
    type SerializeTuple: SerializeTuple<Ok = Self::Ok, Error = Self::Error>;
    type SerializeTupleStruct: SerializeTupleStruct<Ok = Self::Ok, Error = Self::Error>;
    type SerializeTupleVariant: SerializeTupleVariant<Ok = Self::Ok, Error = Self::Error>;
    type SerializeMap: SerializeMap<Ok = Self::Ok, Error = Self::Error>;
    type SerializeStruct: SerializeStruct<Ok = Self::Ok, Error = Self::Error>;
    type SerializeStructVariant: SerializeStructVariant<Ok = Self::Ok, Error = Self::Error>;
    fn serialize_bool(self, v: bool) -> Result<Self::Ok, Self::Error>;

    fn serialize_i8(self, v: i8) -> Result<Self::Ok, Self::Error>;

    fn serialize_i16(self, v: i16) -> Result<Self::Ok, Self::Error>;

    fn serialize_i32(self, v: i32) -> Result<Self::Ok, Self::Error>;

    fn serialize_i64(self, v: i64) -> Result<Self::Ok, Self::Error>;

    fn serialize_u8(self, v: u8) -> Result<Self::Ok, Self::Error>;

    fn serialize_u16(self, v: u16) -> Result<Self::Ok, Self::Error>;

    fn serialize_u32(self, v: u32) -> Result<Self::Ok, Self::Error>;

    fn serialize_u64(self, v: u64) -> Result<Self::Ok, Self::Error>;

    fn serialize_f32(self, v: f32) -> Result<Self::Ok, Self::Error>;

    fn serialize_f64(self, v: f64) -> Result<Self::Ok, Self::Error>;

    fn serialize_char(self, v: char) -> Result<Self::Ok, Self::Error>;

    fn serialize_str(self, v: &str) -> Result<Self::Ok, Self::Error>;

    fn serialize_bytes(self, v: &[u8]) -> Result<Self::Ok, Self::Error>;

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

    fn serialize_some<T: ?Sized>(
        self, 
        value: &T
    ) -> Result<Self::Ok, Self::Error>
    where
        T: Serialize;

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

    fn serialize_unit_struct(
        self, 
        name: &'static str
    ) -> Result<Self::Ok, Self::Error>;

    fn serialize_unit_variant(
        self, 
        name: &'static str, 
        variant_index: u32, 
        variant: &'static str
    ) -> Result<Self::Ok, Self::Error>;

    fn serialize_newtype_struct<T: ?Sized>(
        self, 
        name: &'static str, 
        value: &T
    ) -> Result<Self::Ok, Self::Error>
    where
        T: Serialize;

    fn serialize_newtype_variant<T: ?Sized>(
        self, 
        name: &'static str, 
        variant_index: u32, 
        variant: &'static str, 
        value: &T
    ) -> Result<Self::Ok, Self::Error>
    where
        T: Serialize;

    fn serialize_seq(
        self, 
        len: Option<usize>
    ) -> Result<Self::SerializeSeq, Self::Error>;

    fn serialize_tuple(
        self, 
        len: usize
    ) -> Result<Self::SerializeTuple, Self::Error>;

    fn serialize_tuple_struct(
        self, 
        name: &'static str, 
        len: usize
    ) -> Result<Self::SerializeTupleStruct, Self::Error>;

    fn serialize_tuple_variant(
        self, 
        name: &'static str, 
        variant_index: u32, 
        variant: &'static str, 
        len: usize
    ) -> Result<Self::SerializeTupleVariant, Self::Error>;

    fn serialize_map(
        self, 
        len: Option<usize>
    ) -> Result<Self::SerializeMap, Self::Error>;

    fn serialize_struct(
        self, 
        name: &'static str, 
        len: usize
    ) -> Result<Self::SerializeStruct, Self::Error>;

    fn serialize_struct_variant(
        self, 
        name: &'static str, 
        variant_index: u32, 
        variant: &'static str, 
        len: usize
    ) -> Result<Self::SerializeStructVariant, Self::Error>;

    fn serialize_i128(self, v: i128) -> Result<Self::Ok, Self::Error> { ... }

    fn serialize_u128(self, v: u128) -> Result<Self::Ok, Self::Error> { ... }

    fn collect_seq<I>(self, iter: I) -> Result<Self::Ok, Self::Error>
    where
        I: IntoIterator,
        <I as IntoIterator>::Item: Serialize,
    { ... }

    fn collect_map<K, V, I>(self, iter: I) -> Result<Self::Ok, Self::Error>
    where
        K: Serialize,
        V: Serialize,
        I: IntoIterator<Item = (K, V)>,
    { ... }

    fn collect_str<T: ?Sized>(self, value: &T) -> Result<Self::Ok, Self::Error>
    where
        T: Display,
    { ... }

    fn is_human_readable(&self) -> bool { ... }
}

A data format that can serialize any data structure supported by Serde.

The role of this trait is to define the serialization half of the Serde data model, which is a way to categorize every Rust data structure into one of 29 possible types. Each method of the Serializer trait corresponds to one of the types of the data model.

Implementations of Serialize map themselves into this data model by invoking exactly one of the Serializer methods.

The types that make up the Serde data model are:

Many Serde serializers produce text or binary data as output, for example JSON or Bincode. This is not a requirement of the Serializer trait, and there are serializers that do not produce text or binary output. One example is the serde_json::value::Serializer (distinct from the main serde_json serializer) that produces a serde_json::Value data structure in memory as output.

Example implementation

The example data format presented on the website contains example code for a basic JSON Serializer.

Associated Types

The output type produced by this Serializer during successful serialization. Most serializers that produce text or binary output should set Ok = () and serialize into an io::Write or buffer contained within the Serializer instance. Serializers that build in-memory data structures may be simplified by using Ok to propagate the data structure around.

The error type when some error occurs during serialization.

Type returned from serialize_seq for serializing the content of the sequence.

Type returned from serialize_tuple for serializing the content of the tuple.

Type returned from serialize_tuple_struct for serializing the content of the tuple struct.

Type returned from serialize_tuple_variant for serializing the content of the tuple variant.

Type returned from serialize_map for serializing the content of the map.

Type returned from serialize_struct for serializing the content of the struct.

Type returned from serialize_struct_variant for serializing the content of the struct variant.

Required Methods

Serialize a bool value.

impl Serialize for bool {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_bool(*self)
    }
}

Serialize an i8 value.

If the format does not differentiate between i8 and i64, a reasonable implementation would be to cast the value to i64 and forward to serialize_i64.

impl Serialize for i8 {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_i8(*self)
    }
}

Serialize an i16 value.

If the format does not differentiate between i16 and i64, a reasonable implementation would be to cast the value to i64 and forward to serialize_i64.

impl Serialize for i16 {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_i16(*self)
    }
}

Serialize an i32 value.

If the format does not differentiate between i32 and i64, a reasonable implementation would be to cast the value to i64 and forward to serialize_i64.

impl Serialize for i32 {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_i32(*self)
    }
}

Serialize an i64 value.

impl Serialize for i64 {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_i64(*self)
    }
}

Serialize a u8 value.

If the format does not differentiate between u8 and u64, a reasonable implementation would be to cast the value to u64 and forward to serialize_u64.

impl Serialize for u8 {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_u8(*self)
    }
}

Serialize a u16 value.

If the format does not differentiate between u16 and u64, a reasonable implementation would be to cast the value to u64 and forward to serialize_u64.

impl Serialize for u16 {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_u16(*self)
    }
}

Serialize a u32 value.

If the format does not differentiate between u32 and u64, a reasonable implementation would be to cast the value to u64 and forward to serialize_u64.

impl Serialize for u32 {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_u32(*self)
    }
}

Serialize a u64 value.

impl Serialize for u64 {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_u64(*self)
    }
}

Serialize an f32 value.

If the format does not differentiate between f32 and f64, a reasonable implementation would be to cast the value to f64 and forward to serialize_f64.

impl Serialize for f32 {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_f32(*self)
    }
}

Serialize an f64 value.

impl Serialize for f64 {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_f64(*self)
    }
}

Serialize a character.

If the format does not support characters, it is reasonable to serialize it as a single element str or a u32.

impl Serialize for char {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_char(*self)
    }
}

Serialize a &str.

impl Serialize for str {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_str(self)
    }
}

Serialize a chunk of raw byte data.

Enables serializers to serialize byte slices more compactly or more efficiently than other types of slices. If no efficient implementation is available, a reasonable implementation would be to forward to serialize_seq. If forwarded, the implementation looks usually just like this:

fn serialize_bytes(self, v: &[u8]) -> Result<Self::Ok, Self::Error> {
    let mut seq = self.serialize_seq(Some(v.len()))?;
    for b in v {
        seq.serialize_element(b)?;
    }
    seq.end()
}

Serialize a None value.

impl<T> Serialize for Option<T>
where
    T: Serialize,
{
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        match *self {
            Some(ref value) => serializer.serialize_some(value),
            None => serializer.serialize_none(),
        }
    }
}

Serialize a Some(T) value.

impl<T> Serialize for Option<T>
where
    T: Serialize,
{
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        match *self {
            Some(ref value) => serializer.serialize_some(value),
            None => serializer.serialize_none(),
        }
    }
}

Serialize a () value.

impl Serialize for () {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_unit()
    }
}

Serialize a unit struct like struct Unit or PhantomData<T>.

A reasonable implementation would be to forward to serialize_unit.

use serde::{Serialize, Serializer};

struct Nothing;

impl Serialize for Nothing {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_unit_struct("Nothing")
    }
}

Serialize a unit variant like E::A in enum E { A, B }.

The name is the name of the enum, the variant_index is the index of this variant within the enum, and the variant is the name of the variant.

use serde::{Serialize, Serializer};

enum E {
    A,
    B,
}

impl Serialize for E {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        match *self {
            E::A => serializer.serialize_unit_variant("E", 0, "A"),
            E::B => serializer.serialize_unit_variant("E", 1, "B"),
        }
    }
}

Serialize a newtype struct like struct Millimeters(u8).

Serializers are encouraged to treat newtype structs as insignificant wrappers around the data they contain. A reasonable implementation would be to forward to value.serialize(self).

use serde::{Serialize, Serializer};

struct Millimeters(u8);

impl Serialize for Millimeters {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_newtype_struct("Millimeters", &self.0)
    }
}

Serialize a newtype variant like E::N in enum E { N(u8) }.

The name is the name of the enum, the variant_index is the index of this variant within the enum, and the variant is the name of the variant. The value is the data contained within this newtype variant.

use serde::{Serialize, Serializer};

enum E {
    M(String),
    N(u8),
}

impl Serialize for E {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        match *self {
            E::M(ref s) => serializer.serialize_newtype_variant("E", 0, "M", s),
            E::N(n) => serializer.serialize_newtype_variant("E", 1, "N", &n),
        }
    }
}

Begin to serialize a variably sized sequence. This call must be followed by zero or more calls to serialize_element, then a call to end.

The argument is the number of elements in the sequence, which may or may not be computable before the sequence is iterated. Some serializers only support sequences whose length is known up front.

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

impl<T> Serialize for Vec<T>
where
    T: Serialize,
{
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        let mut seq = serializer.serialize_seq(Some(self.len()))?;
        for element in self {
            seq.serialize_element(element)?;
        }
        seq.end()
    }
}

Begin to serialize a statically sized sequence whose length will be known at deserialization time without looking at the serialized data. This call must be followed by zero or more calls to serialize_element, then a call to end.

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

impl<A, B, C> Serialize for (A, B, C)
where
    A: Serialize,
    B: Serialize,
    C: Serialize,
{
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        let mut tup = serializer.serialize_tuple(3)?;
        tup.serialize_element(&self.0)?;
        tup.serialize_element(&self.1)?;
        tup.serialize_element(&self.2)?;
        tup.end()
    }
}
use serde::ser::{Serialize, Serializer, SerializeTuple};

const VRAM_SIZE: usize = 386;
struct Vram([u16; VRAM_SIZE]);

impl Serialize for Vram {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        let mut seq = serializer.serialize_tuple(VRAM_SIZE)?;
        for element in &self.0[..] {
            seq.serialize_element(element)?;
        }
        seq.end()
    }
}

Begin to serialize a tuple struct like struct Rgb(u8, u8, u8). This call must be followed by zero or more calls to serialize_field, then a call to end.

The name is the name of the tuple struct and the len is the number of data fields that will be serialized.

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

struct Rgb(u8, u8, u8);

impl Serialize for Rgb {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        let mut ts = serializer.serialize_tuple_struct("Rgb", 3)?;
        ts.serialize_field(&self.0)?;
        ts.serialize_field(&self.1)?;
        ts.serialize_field(&self.2)?;
        ts.end()
    }
}

Begin to serialize a tuple variant like E::T in enum E { T(u8, u8) }. This call must be followed by zero or more calls to serialize_field, then a call to end.

The name is the name of the enum, the variant_index is the index of this variant within the enum, the variant is the name of the variant, and the len is the number of data fields that will be serialized.

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

enum E {
    T(u8, u8),
    U(String, u32, u32),
}

impl Serialize for E {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        match *self {
            E::T(ref a, ref b) => {
                let mut tv = serializer.serialize_tuple_variant("E", 0, "T", 2)?;
                tv.serialize_field(a)?;
                tv.serialize_field(b)?;
                tv.end()
            }
            E::U(ref a, ref b, ref c) => {
                let mut tv = serializer.serialize_tuple_variant("E", 1, "U", 3)?;
                tv.serialize_field(a)?;
                tv.serialize_field(b)?;
                tv.serialize_field(c)?;
                tv.end()
            }
        }
    }
}

Begin to serialize a map. This call must be followed by zero or more calls to serialize_key and serialize_value, then a call to end.

The argument is the number of elements in the map, which may or may not be computable before the map is iterated. Some serializers only support maps whose length is known up front.

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

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()
    }
}

Begin to serialize a struct like struct Rgb { r: u8, g: u8, b: u8 }. This call must be followed by zero or more calls to serialize_field, then a call to end.

The name is the name of the struct and the len is the number of data fields that will be serialized.

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

struct Rgb {
    r: u8,
    g: u8,
    b: u8,
}

impl Serialize for Rgb {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        let mut rgb = serializer.serialize_struct("Rgb", 3)?;
        rgb.serialize_field("r", &self.r)?;
        rgb.serialize_field("g", &self.g)?;
        rgb.serialize_field("b", &self.b)?;
        rgb.end()
    }
}

Begin to serialize a struct variant like E::S in enum E { S { r: u8, g: u8, b: u8 } }. This call must be followed by zero or more calls to serialize_field, then a call to end.

The name is the name of the enum, the variant_index is the index of this variant within the enum, the variant is the name of the variant, and the len is the number of data fields that will be serialized.

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

enum E {
    S { r: u8, g: u8, b: u8 }
}

impl Serialize for E {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        match *self {
            E::S { ref r, ref g, ref b } => {
                let mut sv = serializer.serialize_struct_variant("E", 0, "S", 3)?;
                sv.serialize_field("r", r)?;
                sv.serialize_field("g", g)?;
                sv.serialize_field("b", b)?;
                sv.end()
            }
        }
    }
}

Provided Methods

Serialize an i128 value.

impl Serialize for i128 {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_i128(*self)
    }
}

This method is available only on Rust compiler versions >=1.26. The default behavior unconditionally returns an error.

Serialize a u128 value.

impl Serialize for u128 {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_u128(*self)
    }
}

This method is available only on Rust compiler versions >=1.26. The default behavior unconditionally returns an error.

Collect an iterator as a sequence.

The default implementation serializes each item yielded by the iterator using serialize_seq. Implementors should not need to override this method.

use serde::{Serialize, Serializer};

struct SecretlyOneHigher {
    data: Vec<i32>,
}

impl Serialize for SecretlyOneHigher {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.collect_seq(self.data.iter().map(|x| x + 1))
    }
}

Collect an iterator as a map.

The default implementation serializes each pair yielded by the iterator using serialize_map. Implementors should not need to override this method.

use std::collections::BTreeSet;
use serde::{Serialize, Serializer};

struct MapToUnit {
    keys: BTreeSet<i32>,
}

// Serializes as a map in which the values are all unit.
impl Serialize for MapToUnit {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.collect_map(self.keys.iter().map(|k| (k, ())))
    }
}

Serialize a string produced by an implementation of Display.

The default implementation builds a heap-allocated String and delegates to serialize_str. Serializers are encouraged to provide a more efficient implementation if possible.

use serde::{Serialize, Serializer};

impl Serialize for DateTime {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.collect_str(&format_args!("{:?}{:?}",
                                             self.naive_local(),
                                             self.offset()))
    }
}

Determine whether Serialize implementations should serialize in human-readable form.

Some types have a human-readable form that may be somewhat expensive to construct, as well as a binary form that is compact and efficient. Generally text-based formats like JSON and YAML will prefer to use the human-readable one and binary formats like Bincode will prefer the compact one.

use serde::{Serialize, Serializer};

impl Serialize for Timestamp {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        if serializer.is_human_readable() {
            // Serialize to a human-readable string "2015-05-15T17:01:00Z".
            self.to_string().serialize(serializer)
        } else {
            // Serialize to a compact binary representation.
            self.seconds_since_epoch().serialize(serializer)
        }
    }
}

The default implementation of this method returns true. Data formats may override this to false to request a compact form for types that support one. Note that modifying this method to change a format from human-readable to compact or vice versa should be regarded as a breaking change, as a value serialized in human-readable mode is not required to deserialize from the same data in compact mode.

Implementors