[英]Rust: why do I get error [E0507]: cannot move out of `files.input_file` which is behind a shared reference
I have narrowed down my real life Rust code to the following:我已将现实生活中的 Rust 代码缩小为以下内容:
use std::fs::File;
use std::io::{BufRead, BufReader};
struct FileHandler {
input_file: File,
}
impl FileHandler {
fn setup(in_file_name: &str) -> Self {
let i_file = File::open(in_file_name).unwrap();
Self { input_file: i_file }
}
}
fn process_file(files: &FileHandler) {
let lines = BufReader::new(files.input_file).lines();
for _ln in lines {
println!("one more line");
}
}
fn main() {
let files = FileHandler::setup("foo.txt");
process_file(&files);
}
It does not compile with the message:它不编译消息:
cannot move out of `files.input_file` which is behind a shared reference
--> demo.rs:16:32
|
16 | let lines = BufReader::new(files.input_file).lines();
| ^^^^^^^^^^^^^^^^ move occurs because `files.input_file` has type `File`, which does not implement the `Copy` trait
But precisely, I don't want to make a copy.但准确地说,我不想复制。 I just want to use the file I have already checked to be correct.我只想使用我已经检查过的文件。 I have tried with mutable references and fields.我尝试使用可变引用和字段。 Same error.同样的错误。
As the error implies, BufReader::new
is attempting to move files.input_files
, which is behind a shared reference ( &FileHandler
).正如错误所暗示的那样, BufReader::new
正在尝试移动files.input_files
,它位于共享引用 ( &FileHandler
) 之后。 In order to have it not move files.input_file
, use a reference to it instead:为了让它不移动files.input_file
,请改用对它的引用:
use std::fs::File;
use std::io::{BufRead, BufReader};
struct FileHandler {
input_file: File,
}
impl FileHandler {
fn setup(in_file_name: &str) -> Self {
let i_file = File::open(in_file_name).unwrap();
Self { input_file: i_file }
}
}
fn process_file(files: &FileHandler) {
// --- CHANGED ---
let lines = BufReader::new(&files.input_file).lines();
for _ln in lines {
println!("one more line");
}
}
fn main() {
let files = FileHandler::setup("foo.txt");
process_file(&files);
}
This happens because BufReader is generic.发生这种情况是因为BufReader是通用的。 If you give it a value, it will move it, if you give it a reference it'll just use the reference instead.如果你给它一个值,它会移动它,如果你给它一个引用,它只会使用引用。 Take a look at " Understanding Ownership " from The Book for more information on how ownership works.查看 The Book 中的“ Understanding Ownership ”,了解有关所有权如何运作的更多信息。
let files = FileHandler::setup("foo.txt");
This creates a FileHandler
struct which stores another struct called File
in input_file
property.这将创建一个FileHandler
结构,它在input_file
属性中存储另一个名为File
的结构。
files
struct has the ownership of it's properties. files
结构拥有其属性的所有权。 So files
owns input_file
.所以files
拥有input_file
。
If you directly use that input_file
property like this:如果您像这样直接使用该input_file
属性:
some_function(files.input_file);
This means input_file
's ownership will be moved to that function.这意味着input_file
的所有权将移至该 function。
But if you do this then what happens if I try to access files.input_file
again?但是如果你这样做那么如果我再次尝试访问files.input_file
会发生什么? Maybe inside of some_function
, the struct stored in input_file
property destroyed?也许在some_function
内部,存储在input_file
属性中的结构被破坏了?
So I can't use it anymore like files.input_file
.所以我不能再像files.input_file
那样使用它了。
Use the reference of input_file
, so it is borrowed , not moved :使用input_file
的引用,所以它是借用的,而不是移动的:
some_function(&files.input_file);
Or in this case of yours:或者在你的这种情况下:
BufReader::new(&files.input_file);
(btw IMHO I can suggest that you can use new
instead of setup
. Creating a struct with some settings often managed by a new
function. FileHandler::new()
is much more familiar to Rust devs. Like BufReader::new()
) (顺便说一句,恕我直言,我建议您可以使用new
而不是setup
。使用通常由new
的 function 管理的一些设置创建结构。FileHandler FileHandler::new()
对 Rust 开发人员来说更为熟悉。比如BufReader::new()
)
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