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use serde::{ self, de::{Deserializer, MapAccess, Visitor}, ser::{SerializeMap, Serializer}, Deserialize, Serialize, }; use std::{fmt, marker::PhantomData}; pub trait KeyValueLike { type Key; type Value; fn from_key_value(key: Self::Key, value: Self::Value) -> Self; fn key(&self) -> &Self::Key; fn value(&self) -> &Self::Value; } struct KeyValueVecMapVisitor<T: KeyValueLike> { marker: PhantomData<fn() -> Vec<T>>, } impl<T: KeyValueLike> KeyValueVecMapVisitor<T> { fn new() -> Self { Self { marker: PhantomData, } } } impl<'de, T: KeyValueLike, K, V> Visitor<'de> for KeyValueVecMapVisitor<T> where T: KeyValueLike<Key = K, Value = V>, K: Deserialize<'de>, V: Deserialize<'de>, { type Value = Vec<T>; fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result { formatter.write_str("key value map") } fn visit_map<M>(self, mut access: M) -> Result<Self::Value, M::Error> where M: MapAccess<'de>, { let mut vec = Vec::with_capacity(access.size_hint().unwrap_or(0)); while let Some((key, value)) = access.next_entry()? { vec.push(T::from_key_value(key, value)); } Ok(vec) } } pub fn deserialize<'de, D, T, K, V>(deserializer: D) -> Result<Vec<T>, D::Error> where D: Deserializer<'de>, T: KeyValueLike<Key = K, Value = V>, K: Deserialize<'de>, V: Deserialize<'de>, { deserializer.deserialize_map(KeyValueVecMapVisitor::new()) } pub fn serialize<S, T, K, V>(pairs: &Vec<T>, serializer: S) -> Result<S::Ok, S::Error> where S: Serializer, T: KeyValueLike<Key = K, Value = V>, K: Serialize, V: Serialize, { let mut map = serializer.serialize_map(Some(pairs.len()))?; for pair in pairs { map.serialize_entry(pair.key(), pair.value())?; } map.end() } #[cfg(test)] mod tests { use super::*; #[test] fn test_deserialize_with() { let json = r#" { "temperature": 40, "pressure": 123 } "#; #[derive(Debug, Eq, PartialEq)] struct SingleMeasurement { name: String, value: u32, } impl KeyValueLike for SingleMeasurement { type Key = String; type Value = u32; fn from_key_value(key: Self::Key, value: Self::Value) -> Self { Self { name: key, value } } fn key(&self) -> &Self::Key { &self.name } fn value(&self) -> &Self::Value { &self.value } } #[derive(Deserialize)] struct S { #[serde(flatten)] #[serde(with = "crate")] measurements: Vec<SingleMeasurement>, } let s: S = serde_json::from_str(json).unwrap(); assert_eq!( s.measurements, vec![ SingleMeasurement { name: "temperature".into(), value: 40 }, SingleMeasurement { name: "pressure".into(), value: 123 }, ] ); } #[test] fn test_serialize_with() { #[derive(Debug, Eq, PartialEq)] struct SingleMeasurement { name: String, value: u32, } impl KeyValueLike for SingleMeasurement { type Key = String; type Value = u32; fn from_key_value(key: Self::Key, value: Self::Value) -> Self { Self { name: key, value } } fn key(&self) -> &Self::Key { &self.name } fn value(&self) -> &Self::Value { &self.value } } #[derive(Serialize)] struct S { #[serde(flatten)] #[serde(with = "crate")] measurements: Vec<SingleMeasurement>, } let s = S { measurements: vec![ SingleMeasurement { name: "temperature".into(), value: 40, }, SingleMeasurement { name: "pressure".into(), value: 123, }, ], }; assert_eq!( &serde_json::to_string(&s).unwrap(), r#"{"temperature":40,"pressure":123}"# ); } }