csv - 尝试写入 CSV 记录时出现错误 "the trait ` std::convert::AsRef<[u8] >` is not implemented for ` u 8`"

Question

这是一个最小的重现:

extern crate csv;
use std::fs::File;
use std::io::Write;

fn do_write(writer: &mut csv::Writer<File>, buf: &[u8]) {
    // The error is coming from this line
    writer.write_record(buf);
}

fn main() {
    let mut writer = csv::Writer::from_path(r"c:\temp\file.csv").unwrap();
    let str = "Hello, World!".to_string();
    do_write(&mut writer, str.as_bytes());
}

导致编译错误:

error[E0277]: the trait bound `u8: std::convert::AsRef<[u8]>` is not satisfied
 --> src/main.rs:7:16
  |
7 |         writer.write_record(buf);
  |                ^^^^^^^^^^^^ the trait `std::convert::AsRef<[u8]>` is not implemented for `u8`
  |
  = note: required because of the requirements on the impl of `std::convert::AsRef<[u8]>` for `&u8`

这个错误是什么意思？看来我已经传递了一个 u8 切片？

Answer 1

检查 write_record 的签名:

fn write_record<I, T>(&mut self, record: I) -> Result<()> 
where
    I: IntoIterator<Item = T>,
    T: AsRef<[u8]>, 

它期望某些东西可以成为值的迭代器。您正在提供 &[u8] ，它是一个迭代器，但只有&u8值。错误是这些 &u8 s 不执行 AsRef<[u8]> .

您可以将单个传入的字符串包装在另一个数组中以创建可以充当迭代器的东西:

writer.write_record(&[buf]);