p3-util 0.6.1

A collection of utility functions and tools for low-level operations, such as bit manipulation and array transformations.
Documentation 
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use alloc::vec::Vec;
use core::marker::PhantomData;

use serde::de::{SeqAccess, Visitor};
use serde::ser::SerializeTuple;
use serde::{Deserialize, Deserializer, Serialize, Serializer};

pub fn serialize<S: Serializer, T: Serialize, const N: usize>(
    data: &[T; N],
    ser: S,
) -> Result<S::Ok, S::Error> {
    let mut s = ser.serialize_tuple(N)?;
    for item in data {
        s.serialize_element(item)?;
    }
    s.end()
}

struct ArrayVisitor<T, const N: usize>(PhantomData<T>);

impl<'de, T, const N: usize> Visitor<'de> for ArrayVisitor<T, N>
where
    T: Deserialize<'de>,
{
    type Value = [T; N];

    fn expecting(&self, formatter: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        formatter.write_fmt(format_args!("an array of length {N}"))
    }

    #[inline]
    fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
    where
        A: SeqAccess<'de>,
    {
        let mut data = Vec::with_capacity(N);
        for _ in 0..N {
            match seq.next_element()? {
                Some(val) => data.push(val),
                None => return Err(serde::de::Error::invalid_length(data.len(), &self)),
            }
        }
        data.try_into().map_or_else(|_| unreachable!(), Ok)
    }
}
pub fn deserialize<'de, D, T, const N: usize>(deserializer: D) -> Result<[T; N], D::Error>
where
    D: Deserializer<'de>,
    T: Deserialize<'de>,
{
    deserializer.deserialize_tuple(N, ArrayVisitor::<T, N>(PhantomData))
}

#[cfg(test)]
mod tests {
    use serde::{Deserialize, Serialize};
    use serde_json;

    use super::*;

    /// A helper wrapper struct to use serialize/deserialize hooks on arrays.
    #[derive(Serialize, Deserialize, Debug, PartialEq)]
    #[serde(bound(serialize = "", deserialize = ""))]
    struct Wrapper<const N: usize> {
        #[serde(serialize_with = "serialize", deserialize_with = "deserialize")]
        arr: [u32; N],
    }

    #[test]
    fn test_array_serde_roundtrip() {
        let original = Wrapper::<3> { arr: [10, 20, 30] };

        let json = serde_json::to_string(&original).unwrap();
        assert_eq!(json, r#"{"arr":[10,20,30]}"#);

        let deserialized: Wrapper<3> = serde_json::from_str(&json).unwrap();
        assert_eq!(deserialized, original);

        let parsed: Wrapper<3> = serde_json::from_str(r#"{"arr":[10,20,30]}"#).unwrap();
        assert_eq!(parsed.arr, [10, 20, 30]);
    }

    #[test]
    fn test_deserialize_wrong_length() {
        let json = r#"{"arr":[1,2]}"#;

        let result: Result<Wrapper<3>, _> = serde_json::from_str(json);
        assert!(result.is_err());
    }

    #[test]
    fn test_empty_array() {
        let data = Wrapper::<0> { arr: [] };

        let json = serde_json::to_string(&data).unwrap();
        assert_eq!(json, r#"{"arr":[]}"#);

        let parsed: Wrapper<0> = serde_json::from_str(&json).unwrap();
        assert_eq!(parsed, data);
    }
}