Struct serde_with::PickFirst

pub struct PickFirst<T>(_);

Try multiple deserialization options until one succeeds.

This adapter allows you to specify a list of deserialization options. They are tried in order and the first one working is applied. Serialization always picks the first option.

PickFirst has one type parameter which must be instanciated with a tuple of two, three, or four elements. For example, PickFirst<(_, DisplayFromStr)> on a field of type u32 allows to deserialize from a number or from a string via the FromStr trait. The value will be serialized as a number, since that is what the first type _ indicates.

Examples

Deserialize a number from either a number or a string.

#[serde_as]
#[derive(Deserialize, serde::Serialize)]
struct Data {
    #[serde_as(as = "PickFirst<(_, DisplayFromStr)>")]
    as_number: u32,
    #[serde_as(as = "PickFirst<(DisplayFromStr, _)>")]
    as_string: u32,
}
let data = Data {
    as_number: 123,
    as_string: 456
};

// Both fields can be deserialized from numbers:
let j = json!({
    "as_number": 123,
    "as_string": 456,
});
assert_eq!(data, serde_json::from_value(j).unwrap());

// or from a string:
let j = json!({
    "as_number": "123",
    "as_string": "456",
});
assert_eq!(data, serde_json::from_value(j).unwrap());

// For serialization the first type in the tuple determines the behavior.
// The `as_number` field will use the normal `Serialize` behavior and produce a number,
// while `as_string` used `Display` to produce a string.
let expected = json!({
    "as_number": 123,
    "as_string": "456",
});
assert_eq!(expected, serde_json::to_value(&data).unwrap());

Trait Implementations

impl<T: Clone> Clone for PickFirst<T>

fn clone(&self) -> PickFirst<T>

Returns a copy of the value.

pub fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: Copy> Copy for PickFirst<T>

impl<T: Debug> Debug for PickFirst<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T: Default> Default for PickFirst<T>

fn default() -> PickFirst<T>

Returns the “default value” for a type.

impl<'de, T, TAs1> DeserializeAs<'de, T> for PickFirst<(TAs1,)> where
    TAs1: DeserializeAs<'de, T>, 

fn deserialize_as<D>(deserializer: D) -> Result<T, D::Error> where
    D: Deserializer<'de>, 

Deserialize this value from the given Serde deserializer.

impl<'de, T, TAs1, TAs2> DeserializeAs<'de, T> for PickFirst<(TAs1, TAs2)> where
    TAs1: DeserializeAs<'de, T>,
    TAs2: DeserializeAs<'de, T>, 

fn deserialize_as<D>(deserializer: D) -> Result<T, D::Error> where
    D: Deserializer<'de>, 

Deserialize this value from the given Serde deserializer.

impl<'de, T, TAs1, TAs2, TAs3> DeserializeAs<'de, T> for PickFirst<(TAs1, TAs2, TAs3)> where
    TAs1: DeserializeAs<'de, T>,
    TAs2: DeserializeAs<'de, T>,
    TAs3: DeserializeAs<'de, T>, 

fn deserialize_as<D>(deserializer: D) -> Result<T, D::Error> where
    D: Deserializer<'de>, 

Deserialize this value from the given Serde deserializer.

impl<'de, T, TAs1, TAs2, TAs3, TAs4> DeserializeAs<'de, T> for PickFirst<(TAs1, TAs2, TAs3, TAs4)> where
    TAs1: DeserializeAs<'de, T>,
    TAs2: DeserializeAs<'de, T>,
    TAs3: DeserializeAs<'de, T>,
    TAs4: DeserializeAs<'de, T>, 

fn deserialize_as<D>(deserializer: D) -> Result<T, D::Error> where
    D: Deserializer<'de>, 

Deserialize this value from the given Serde deserializer.

impl<T, TAs1> SerializeAs<T> for PickFirst<(TAs1,)> where
    TAs1: SerializeAs<T>, 

fn serialize_as<S>(source: &T, serializer: S) -> Result<S::Ok, S::Error> where
    S: Serializer, 

Serialize this value into the given Serde serializer.

impl<T, TAs1, TAs2> SerializeAs<T> for PickFirst<(TAs1, TAs2)> where
    TAs1: SerializeAs<T>, 

fn serialize_as<S>(source: &T, serializer: S) -> Result<S::Ok, S::Error> where
    S: Serializer, 

Serialize this value into the given Serde serializer.

impl<T, TAs1, TAs2, TAs3> SerializeAs<T> for PickFirst<(TAs1, TAs2, TAs3)> where
    TAs1: SerializeAs<T>, 

fn serialize_as<S>(source: &T, serializer: S) -> Result<S::Ok, S::Error> where
    S: Serializer, 

Serialize this value into the given Serde serializer.

impl<T, TAs1, TAs2, TAs3, TAs4> SerializeAs<T> for PickFirst<(TAs1, TAs2, TAs3, TAs4)> where
    TAs1: SerializeAs<T>, 

fn serialize_as<S>(source: &T, serializer: S) -> Result<S::Ok, S::Error> where
    S: Serializer, 

Serialize this value into the given Serde serializer.