Shared via Rust Playground

playground.rs

pub struct TextEditor {
    text: String //Private member variable
}
 
impl TextEditor {
    pub fn new() -> TextEditor {
        TextEditor{text: String::new()}
    }
 
    pub fn add_char(&mut self, ch : char) {
        self.text.push(ch);
    }
    
    // Clona o valor em uma nova área de memória. Essa solução é muito cara.
    /**/
    pub fn get_text_clone(&self) -> String {
        self.text.clone()
    }

    // Rust não vai deixar.
    // Esse código implacaria em mudança de ownership causando um provável 'Double free'.
    /*
    pub fn get_text_copy(&self) -> String {
        return self.text
    }
    */
    
    pub fn get_text(&self) -> &String {
        return &self.text;
    }
    
    /* Beghind the scenes...
    pub fn get_text<'a>(&'a self) -> &'a String {
        return &self.text;
    }
    */
    
    pub fn reset(&mut self) {
        self.text = String::new();
    }
}
 
fn main() {
    use_after_free_example();
}
/*
fn good() {
    let mut editor = TextEditor::new();
 
    editor.add_char('a');
    editor.add_char('b');
    editor.add_char('c');

    /* With clone
    let my_txt = editor.get_text_clone();
    */
    
    /* With borrow */
    let my_txt = editor.get_text();
    
    println!("{}", my_txt);
}

fn trouble_in_compile_time() {
    let my_txt;
 
    {
        let mut editor = TextEditor::new();
     
        editor.add_char('a');
        editor.add_char('b');
        editor.add_char('c');
     
        my_txt = editor.get_text();
    } //Variable 'editor' destroyed.
     
    println!("{}", my_txt); //Use after free. Not possible.
}
*/

fn use_after_free_example() {
    let mut editor = TextEditor::new();
 
    editor.add_char('a');
    editor.add_char('b');
    editor.add_char('c');
     
    let my_txt = editor.get_text();
     
    editor.reset();
     
    println!("{}", my_txt); //Use after free. Not possible.
}