变量在存储csv :: DecodedRecords迭代器时不会足够长 [英] variable does not live long enough when storing a csv::DecodedRecords iterator

问题描述

我试图创建一个迭代器trait，提供特定类型的资源，所以我可以实现多种源类型。我想要创建一个源文件从CSV文件，二进制等读取。

I'm trying to create an iterator trait that provides a specific type of resource, so I can implement multiple source types. I'd like to create a source for reading from a CSV file, a binary etc..

我使用 rust-csv 用于反序列化CSV数据的库：

I'm using the rust-csv library for deserializing CSV data:

#[derive(RustcDecodable)]
struct BarRecord {
    bar: u32
}

trait BarSource : Iterator {}

struct CSVBarSource {
    records: csv::DecodedRecords<'static, std::fs::File, BarRecord>,
}

impl CSVBarSource {
    pub fn new(path: String) -> Option<CSVBarSource> {
        match csv::Reader::from_file(path) {
            Ok(reader) => Some(CSVBarSource { records: reader.decode() }),
            Err(_) => None
        }
    }
}

impl Iterator for CSVBarSource {
    type Item = BarRecord;

    fn next(&mut self) -> Option<BarRecord> {
        match self.records.next() {
            Some(Ok(e)) => Some(e),
            _ => None
        }
    }
}

由于生命周期问题，CSV阅读器返回的 DecodedRecords 迭代器的引用：

I cannot seem to store a reference to the DecodedRecords iterator returned by the CSV reader due to lifetime issues:

错误：读取器不够长时间运行

error: reader does not live long enough

如何存储对解码记录迭代器的引用以及我做错了什么？

How can I store a reference to the decoded records iterator and what am I doing wrong?

推荐答案

根据文档， Reader :: decode 定义为：

According to the documentation, Reader::decode is defined as:

fn decode<'a, D: Decodable>(&'a mut self) -> DecodedRecords<'a, R, D>

这是 reader.decode（） outlive reader （因为'a ）。
和这个声明：

That is reader.decode() cannot outlive reader (because of 'a). And with this declaration:

struct CSVBarSource {
    records: csv::DecodedRecords<'static, std::fs::File, BarRecord>,
                              // ^~~~~~~
}

读者需要一个'static 生命周期， ，因此它不会因此您得到的错误阅读器不能居住足够长。

reader would need a 'static lifetime, that is it would need to live forever, which it does not hence the error you get "reader does not live long enough".

直接在中读取 CSVBarSource ：

You should store reader directly in CSVBarSource:

struct CSVBarSource {
    reader: csv::Reader<std::fs::File>,
}

只需根据需要调用 decode 。

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