1 files changed, 78 insertions, 0 deletions
diff --git a/src/serde_untagged_optional.rs b/src/serde_untagged_optional.rs
new file mode 100644
index 0000000..f0cca36
--- /dev/null
+++ b/src/serde_untagged_optional.rs
@@ -0,0 +1,78 @@
+//! Untagged serialization/deserialization support for Option<Either<L, R>>.
+//!
+//! `Either` uses default, externally-tagged representation.
+//! However, sometimes it is useful to support several alternative types.
+//! For example, we may have a field which is generally Map<String, i32>
+//! but in typical cases Vec<String> would suffice, too.
+//!
+//! ```rust
+//! #[macro_use]
+//! extern crate serde;
+//! // or `use serde::{Serialize, Deserialize};` in newer rust versions.
+//!
+//! # fn main() -> Result<(), Box<dyn std::error::Error>> {
+//! use either::Either;
+//! use std::collections::HashMap;
+//!
+//! #[derive(Serialize, Deserialize, Debug)]
+//! #[serde(transparent)]
+//! struct IntOrString {
+//!     #[serde(with = "either::serde_untagged_optional")]
+//!     inner: Option<Either<Vec<String>, HashMap<String, i32>>>
+//! };
+//!
+//! // serialization
+//! let data = IntOrString {
+//!     inner: Some(Either::Left(vec!["Hello".to_string()]))
+//! };
+//! // notice: no tags are emitted.
+//! assert_eq!(serde_json::to_string(&data)?, r#"["Hello"]"#);
+//!
+//! // deserialization
+//! let data: IntOrString = serde_json::from_str(
+//!     r#"{"a": 0, "b": 14}"#
+//! )?;
+//! println!("found {:?}", data);
+//! # Ok(())
+//! # }
+//! ```
+
+use serde::{Deserialize, Deserializer, Serialize, Serializer};
+
+#[derive(Serialize, Deserialize)]
+#[serde(untagged)]
+enum Either<L, R> {
+    Left(L),
+    Right(R),
+}
+
+pub fn serialize<L, R, S>(
+    this: &Option<super::Either<L, R>>,
+    serializer: S,
+) -> Result<S::Ok, S::Error>
+where
+    S: Serializer,
+    L: Serialize,
+    R: Serialize,
+{
+    let untagged = match this {
+        &Some(super::Either::Left(ref left)) => Some(Either::Left(left)),
+        &Some(super::Either::Right(ref right)) => Some(Either::Right(right)),
+        &None => None,
+    };
+    untagged.serialize(serializer)
+}
+
+pub fn deserialize<'de, L, R, D>(deserializer: D) -> Result<Option<super::Either<L, R>>, D::Error>
+where
+    D: Deserializer<'de>,
+    L: Deserialize<'de>,
+    R: Deserialize<'de>,
+{
+    match Option::deserialize(deserializer) {
+        Ok(Some(Either::Left(left))) => Ok(Some(super::Either::Left(left))),
+        Ok(Some(Either::Right(right))) => Ok(Some(super::Either::Right(right))),
+        Ok(None) => Ok(None),
+        Err(error) => Err(error),
+    }
+}