Rust 如何使用 Serde 来序列化大于 32 个元素的数组，例如 [u8; 128]

目前Serde无法提供适用于every数组大小的Serialize和Deserialize IMPL.这是被封锁在const generics，这是正在工作，并有望在2018年晚些时候在夜间降落.

现在，您可以定义自己的"大数组"助手，它可以序列化和反序列化 crate 中使用的任何特定大小的array.要使用大数组帮助器的字段需要标记为#[serde(with = "BigArray")]，否则Serde将查找不存在的Serialize和Deserialize impl.

#[macro_use]
extern crate serde_derive;

extern crate serde;
extern crate bincode;

mod big_array;
use big_array::BigArray;

const BYTECOUNT: usize = 128;
type DataArr = [u8; BYTECOUNT];

#[derive(Serialize, Deserialize)]
struct Entry {
    number: i64,
    #[serde(with = "BigArray")]
    data: DataArr
}

fn main() {
    let mut my_entry = Entry { number: 12345, data: [0; BYTECOUNT] };
    my_entry.data[4] = 42;

    // Convert the Entry to binary.
    let serialized: Vec<u8> = bincode::serialize(&my_entry).unwrap();
    println!("serialized = {:?}", serialized);

    // Convert the binary representation back to an Entry.
    let deserialized: Entry = bincode::deserialize(&serialized).unwrap();
    println!("deserialized = {} {:?}", deserialized.number, &deserialized.data[..]);
}

大数组助手可以在src/big_array.rs中定义如下.如果你想拥有它的话，也许这本身就是一个很好的 crate ！

use std::fmt;
use std::marker::PhantomData;
use serde::ser::{Serialize, Serializer, SerializeTuple};
use serde::de::{Deserialize, Deserializer, Visitor, SeqAccess, Error};

pub trait BigArray<'de>: Sized {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
        where S: Serializer;
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
        where D: Deserializer<'de>;
}

macro_rules! big_array {
    ($($len:expr,)+) => {
        $(
            impl<'de, T> BigArray<'de> for [T; $len]
                where T: Default + Copy + Serialize + Deserialize<'de>
            {
                fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
                    where S: Serializer
                {
                    let mut seq = serializer.serialize_tuple(self.len())?;
                    for elem in &self[..] {
                        seq.serialize_element(elem)?;
                    }
                    seq.end()
                }

                fn deserialize<D>(deserializer: D) -> Result<[T; $len], D::Error>
                    where D: Deserializer<'de>
                {
                    struct ArrayVisitor<T> {
                        element: PhantomData<T>,
                    }

                    impl<'de, T> Visitor<'de> for ArrayVisitor<T>
                        where T: Default + Copy + Deserialize<'de>
                    {
                        type Value = [T; $len];

                        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
                            formatter.write_str(concat!("an array of length ", $len))
                        }

                        fn visit_seq<A>(self, mut seq: A) -> Result<[T; $len], A::Error>
                            where A: SeqAccess<'de>
                        {
                            let mut arr = [T::default(); $len];
                            for i in 0..$len {
                                arr[i] = seq.next_element()?
                                    .ok_or_else(|| Error::invalid_length(i, &self))?;
                            }
                            Ok(arr)
                        }
                    }

                    let visitor = ArrayVisitor { element: PhantomData };
                    deserializer.deserialize_tuple($len, visitor)
                }
            }
        )+
    }
}

big_array! {
    40, 48, 50, 56, 64, 72, 96, 100, 128, 160, 192, 200, 224, 256, 384, 512,
    768, 1024, 2048, 4096, 8192, 16384, 32768, 65536,
}