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use std::fmt;
use std::marker::PhantomData;
use serde::{Deserialize, Deserializer};
use serde::de::{Error, Visitor, IntoDeserializer};
#[derive(Debug, PartialEq, Clone)]
pub enum MaybeEmpty<T> {
Some(T),
None,
}
impl<'a, T> Deserialize<'a> for MaybeEmpty<T> where T: Deserialize<'a> {
fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
where D: Deserializer<'a> {
deserializer.deserialize_any(MaybeEmptyVisitor::new())
}
}
struct MaybeEmptyVisitor<T> {
_phantom: PhantomData<T>
}
impl<T> MaybeEmptyVisitor<T> {
fn new() -> Self {
MaybeEmptyVisitor {
_phantom: PhantomData
}
}
}
impl<'a, T> Visitor<'a> for MaybeEmptyVisitor<T> where T: Deserialize<'a> {
type Value = MaybeEmpty<T>;
fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
write!(formatter, "an empty string or string-encoded type")
}
fn visit_str<E>(self, value: &str) -> Result<Self::Value, E> where E: Error {
self.visit_string(value.to_owned())
}
fn visit_string<E>(self, value: String) -> Result<Self::Value, E> where E: Error {
match value.is_empty() {
true => Ok(MaybeEmpty::None),
false => {
T::deserialize(value.into_deserializer()).map(MaybeEmpty::Some)
}
}
}
}
impl<T> Into<Option<T>> for MaybeEmpty<T> {
fn into(self) -> Option<T> {
match self {
MaybeEmpty::Some(s) => Some(s),
MaybeEmpty::None => None
}
}
}
#[cfg(test)]
mod tests {
use std::str::FromStr;
use serde_json;
use ethereum_types;
use hash::H256;
use maybe::MaybeEmpty;
#[test]
fn maybe_deserialization() {
let s = r#"["", "5a39ed1020c04d4d84539975b893a4e7c53eab6c2965db8bc3468093a31bc5ae"]"#;
let deserialized: Vec<MaybeEmpty<H256>> = serde_json::from_str(s).unwrap();
assert_eq!(deserialized, vec![
MaybeEmpty::None,
MaybeEmpty::Some(H256(ethereum_types::H256::from_str("5a39ed1020c04d4d84539975b893a4e7c53eab6c2965db8bc3468093a31bc5ae").unwrap()))
]);
}
}