rust - Rust:创建结构，借入/生命周期问题的向量时为E0597

Question

我对Rust还是很陌生，并且一直在与所有权机制进行斗争。
我想遍历本地目录并将所有单个元素收集到一个结构中。然后将这些结构放入向量中以备后用。因此，基本上我正在尝试构建结构的向量。
结构的前两个字段应分别包含路径各个部分的向量，后两个字段应为OsString:

struct FileItem<'a> {
        g_base_dir: Vec<Component<'a>>, //base directory
        o_full_uri: Vec<Component<'a>>, //original full path
        o_filename: OsString,           //original filename
        o_extension: OsString,          //original extension
    }

我使用“WalkDir”遍历目录并为每个单独的项目获取“DirEntry”。我的问题是我无法将构造的结构推到向量上:

fn main() {
    let mut file_item_collection: Vec<FileItem> = Vec::new();

    let base_dir = Path::new("D:\\test");

    for entry in WalkDir::new(base_dir).into_iter().filter_map(|e| e.ok()) {
        let current_file = FileItem {
            g_base_dir: base_dir.components().collect::<Vec<_>>(),
            o_full_uri: entry.path().components().collect::<Vec<_>>(),
            o_filename: integrity_check(1, &entry).unwrap(),
            o_extension: integrity_check(2, &entry).unwrap(),
        };

        file_item_collection.push(current_file);
    }

    for item in &file_item_collection {
       println!("{:?}", item.o_full_uri);
    }

o_full_uri的分配失败，因为:

`entry` does not live long enough
borrowed value does not live long enough rustc(E0597)
main.rs(56, 5): `entry` dropped here while still borrowed
main.rs(55, 9): borrow later used here

我知道 entry不在范围内，但是我不知道该怎么办。
任何帮助将不胜感激!

考虑到@Hadus和@kmdreko的输入，解决方案看起来像这样，并且运行良好:

struct FileItem {
    g_base_dir: Vec<OsString>, //global base directory
    o_full_uri: Vec<OsString>, //original full path
    o_filename: OsString,      //original filename
    o_extension: OsString,     //original extension
}

fn main() {
    let mut file_item_collection: Vec<FileItem> = Vec::new();

    let base_dir = Path::new("D:/test");

    let entries: Vec<DirEntry> = WalkDir::new(base_dir)
        .into_iter()
        .filter_map(|e| e.ok())
        .collect();

    for entry in &entries {
        if entry.path().is_file() {
            let current_file = FileItem {
                g_base_dir: base_dir
                    .components()
                    .map(|e| e.as_os_str().to_os_string())
                    .collect(),
                o_full_uri: entry
                    .path()
                    .components()
                    .map(|e| e.as_os_str().to_os_string())
                    .collect(),
                o_filename: entry.path().file_stem().unwrap_or_default().to_os_string(),
                o_extension: entry.path().extension().unwrap_or_default().to_os_string(),
            };
            file_item_collection.push(current_file);
        } else {
            continue;
        }
    }

谢谢!

Answer 1

您对entry的生命周期不够长的问题是正确的。考虑一下这种简化:

let mut things = vec![];

{
    // things inside here live till the end of this scope
    let entry = 7;
        
    // this won't work because entry will be dropped when
    // the scope exits and we would be pointing to nothing
    things.push(&entry);
}

// here entry doesn't exist anymore

问题是您试图将指向内部作用域的引用存储在外部作用域中。您必须仅具有指向相同范围或更高范围的引用。
例如，这很好(范围相同):

let mut things = vec![];

// lives as long as things
let entry = 7;

{
    // this will work
    things.push(&entry);
}

// here entry and things still both exist

这也很好(更高的范围):

// lives longer than things
let entry = 7;

{
    let mut things = vec![];

    // this will work
    things.push(&entry);
}

我们必须确保在 entry循环的末尾(使用相同的作用域)不会丢弃 while:

fn main() {
    let mut file_item_collection: Vec<FileItem> = Vec::new();

    let base_dir = Path::new("D:\\test");

    // the entries are now stored outside the while loop
    // so they do live long enough
    let entries: Vec<DirEntry> = WalkDir::new(base_dir)
        .into_iter()
        .filter_map(|e| e.ok())
        .collect();

    for entry in &entries {
        ...
    }
    
    ...
}