Rust:如何限制派生特征的类型参数

Question

这个问题在这里已经有了答案:





Lifetime error when creating a function that returns a value implementing serde::Deserialize

(2 个回答)


1年前关闭。




我正在尝试编写一个通用函数，该函数采用指向 csv 文件的路径，将文件解析并反序列化为特定类型的记录向量并返回记录向量。

这是我的代码:

[dependencies]
csv = "1.1"
serde = { version = "1.0", features = ["derive"] }

首先是编译好的特定类型版本:

use csv;
use serde::Deserialize;
use std::path::Path;

#[derive(Debug, Deserialize)]
struct Person {
    name: String,
    fav_colour: String,
}

#[derive(Debug, Deserialize)]
struct Car {
    make: String,
    year: u8,
}

fn main() {}

fn parse_csv(file_path: &Path) -> Vec<Person> {
    // Create the csv reader
    let mut csv_reader = csv::Reader::from_path(file_path).unwrap();

    // Parse the csv and collect records
    let records: Vec<Person> = csv_reader
        .deserialize()
        .map(|record: Result<Person, csv::Error>| {
            record.expect(&format!("There was a problem parsing a line"))
        })
        .collect();

    // Return records
    records
}

parse_csv 函数适用于混凝土 Person结构。

我怎样才能重写这个函数，使它接受一个派生反序列化的泛型类型/结构，例如它可以接受 Person或 Car ?

尝试失败:

fn parse_csv<T>(file_path: &Path) -> Vec<T> {
    // Create the csv reader
    let mut csv_reader = csv::Reader::from_path(file_path).unwrap();

    // Parse the csv and collect records
    let records: Vec<T> = csv_reader
        .deserialize()
        .map(|record: Result<T, csv::Error>| {
            record.expect(&format!("There was a problem parsing a line"))
        })
        .collect();

    // Return records
    records
}

产生:

error[E0277]: the trait bound `for<'de> T: _::_serde::Deserialize<'de>` is not satisfied
  --> src/main.rs:26:10
   |
26 |         .map(|record: Result<T, csv::Error>| {
   |          ^^^ the trait `for<'de> _::_serde::Deserialize<'de>` is not implemented for `T`
   |
help: consider restricting this type parameter with `T: for<'de> _::_serde::Deserialize<'de>`
  --> src/main.rs:19:14
   |
19 | fn parse_csv<T>(file_path: &Path) -> Vec<T> {
   |              ^
   = note: required because of the requirements on the impl of `_::_serde::de::DeserializeOwned` for `T`
   = note: required because of the requirements on the impl of `std::iter::Iterator` for `csv::reader::DeserializeRecordsIter<'_, std::fs::File, T>`

编译器提示:

help: consider restricting this type parameter with `T: for<'de> _::_serde::Deserialize<'de>`

我该怎么做呢？
我对 rust 比较陌生，在阅读了 rust book 的 traits and the where clause 信息后(我怀疑答案在哪里)，我仍然无法编译它。

Answer 1

您可以按照以下方式进行操作:

use serde::de::DeserializeOwned;

fn parse_csv<T>(file_path: &Path) -> Vec<T>
where
    T: DeserializeOwned,
{
  /// deserialization logic
}