“结构中的生命周期：”此值要求 `'1` 必须比 `'static` 寿命长

Question

I am new to the concept of lifetime but I don't understand why the current code gives me an error

error -> [1]: https://i.stack.imgur.com/v4Yf6.png

Code:

pub struct Folder<'a> {
    pub name: &'a str,
    pub contents: Vec<Box<dyn Executable>>, 
    pub parent: Box<Option<&'a Folder<'a>>>
}

impl<'a> Folder<'a> {
    pub fn new(folder_name: &'a str, json_content: &'a Value) -> Self {
        Self {
            name: folder_name,
            contents: Folder::get_content(json_content),
            parent: Box::new(None)
        }
    }

    fn get_content(json_content: &Value) -> Vec<Box<dyn Executable>> {
        let elements_in_folder: &Vec<Value> = json_content.as_array().unwrap();
        let mut contents: Vec<Box<dyn Executable>> = Vec::new();

        for element in elements_in_folder.iter() {
            match element["type"].as_str().unwrap() {
                "folder" => {
                    let folder = Folder::new(
                        element["name"].as_str().unwrap(),
                        &element["content"],
                    );
                    contents.push(Box::new(folder))
                }

                "command" => contents.push(Box::new(Command::new(&element))),

                "combo" => contents.push(Box::new(Combo::new(&element))),

                _ => panic!("Folder: field type unknow"),
            }
        }
        contents  // THE ERROR IS HERE 
    }
}

Folder Command and Combo impl Executable

Answer 1

Your contents is borrowing values from inside the argument. You need to make that explicit, with a lifetime constraint.

fn get_content<'a>(json_content: &'a Value) -> Vec<Box<dyn Executable + 'a>> {
  ...
}

or, equivalently, you can use the anonymous lifetime. The following is equivalent to the above but shorter.

fn get_content(json_content: &Value) -> Vec<Box<dyn Executable + '_>> {
  ...
}