在函数之间传递BufReader/BufWriter的惯用方式是什么? [英] Whats the idiomatic way to reference BufReader/BufWriter when passing it between functions?
问题描述
阅读 std::io::BufReader 文档后，我我不确定如何在函数之间最好地传递BufReader.允许进行多种排列，但是哪一个是最好的?
After reading the std::io::BufReader docs, I'm not sure how to best pass a BufReader between functions. Multiple permutations are allowed, but which is best?
我有一个带文件的功能:
I have a function that takes a file:
use std::{fs::File, io::BufReader};
fn write_some_data(f: &mut std::fs::File) {
let mut reader = BufReader::new(f);
write_some_other_data(&mut reader);
}
这可以使之起作用，但是当将阅读器传递给其他功能时，应该使用哪种引用访问权限排列?
While this can be made to work, which permutation of reference access should be used when passing the reader around to other functions?
-
&mut BufReader<&mut File> -
BufReader<&mut File> -
&mut BufReader<File> -
BufReader<File>
&mut BufReader<&mut File>BufReader<&mut File>&mut BufReader<File>BufReader<File>
由于我不需要每个函数都拥有数据，因此我认为最好以&mut BufReader<&mut File>的形式传递，但是文档中的示例使用了<File>.
Since there is no need for each function to own the data I was thinking it would be best to pass as &mut BufReader<&mut File>, but the example in the docs uses <File>.
在这里使用一条好的经验法则是什么?
Whats a good rule of thumb to use here?
尽管此示例使用BufReader，但我想同样的答案也适用于BufWriter.
While this example uses BufReader, I assume the same answer would apply to BufWriter too.
推荐答案
最惯用的方式可能是根本不引用std::io::BufReader.您实际上要引用特征Read和/或BufRead
The most idiomatic way is probably not to reference std::io::BufReader at all. You actually want to refer to the traits Read and/or BufRead
use std::io:BufRead;
// Could also take by move if needed
fn read_data<R: BufRead>(r: &mut R);
该函数通常并不真正在乎读取器是否是std::io::BufReader类型，只是它具有相同的功能.
The function usually doesn't really care whether a reader is specifically the type std::io::BufReader, merely that it has the same functionality.
这也使您可以完全自由地选择BufReader<File>，BufReader<&mut File>或所需的其他任何专业. (它甚至不必是一个文件，可以帮助进行测试！)
This also gives you complete freedom to choose between BufReader<File>, BufReader<&mut File> or whichever other specialization you need. (It doesn't even have to be a file, which can help for testing!)
关于是否使用&mut而不是移动，通常在Rust中，标准是仅请求您需要的内容.如果您(和您调用的函数)仅需要一个不变的引用(&T)，请使用该引用，如果您需要可变性，请使用&mut T.
As for whether to use &mut versus a move, generally in Rust it's standard to only request what you need. If you (and the functions you call) only require an immutable reference (&T), use that, if you require mutability, use &mut T.
Move稍微灵活一点，因为虽然可以根据是否需要使用按值获取值的函数来简单地使用它，但是它也经常被用来断言该函数会消耗"某些数据.道路.
Move is a bit more flexible, because while it can be used simply based on whether you need to use a function that takes something by value, it's also frequently used to assert that the function will "use up" the data in some way.
这就是为什么BufReader通常采用File而不是引用的原因，以及为什么大多数高级解析此文件" IO功能倾向于按值移动.通常情况下，您不会使用一个适配器消耗File或阅读器的一部分，而使用另一个适配器消耗其余的.
This is why BufReader usually takes a File and not a reference, and why most high-level "parse this file" IO functions tend to move by value. It's generally not the case that you consume part of a File or reader with one adapter, and the rest with another.
实际上，这在概念上是如此强大，以至于没有给出参考，更常见的是将File移到更高级别的阅读器中，并在需要时调用into_inner之类的函数来检索文件.切换适配器.
In fact, this is conceptually so strong that rather than giving a reference, it's much more common to just move the File into a higher-level reader and call a function like into_inner to retrieve the file whenever you need to switch adapters.
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