ownership

We all know that returning a reference to a local variable is a bad idea . However, I'm wondering if it's ever really a good idea to a return a reference at all and if it's possible to determine some good rules about when or when not to do it. My problem with returning a reference is that the calling function needs to care about the lifetime of an object that shouldn't be its responsibility. As a contrived example: #include <vector> const int& foo() { std::vector<int> v = {1, 2, 3, 4, 5}; return v[0]; } int main(int argc, const char* argv[]) { const int& not_valid = foo(); return 0; } Here,

I just provided an answer for this question and wanted to provide a working example when I noticed that newly created QMimeData instance returned by QListModel::mimeData() won't get deleted until the application gets terminated. So this is not a real memory leak since Qt handles all QMimeData instances on shutdown but you only have to drag&drop long enough and put the right content into your mime data to let the memory run full. Did I miss something? Is there a way to tell Qt to delete the QMimeData instances as soon as they are not needed any more? Please note: I know that every instance of

I've just written a small Rust program which calculates Fibonacci numbers and memoizes the calculation. It works, but I'm a little confused about why, especially the recursive call. (It also probably isn't idiomatic.) Here's the program: use std::collections::HashMap; fn main() { let n = 42; // hardcoded for simplicity let mut cache = HashMap::new(); let answer = fib(n, &mut cache); println!("fib of {} is {}", n, answer); } fn fib(n: i32, cache: &mut HashMap<i32,i32>) -> i32 { if cache.contains_key(&n) { return cache[&n]; } else { if n < 1 { panic!("must be >= 1") } let answer = if n == 1 { 0

I have a script giving me error 403 Forbidden error , it's just a copy of another script but the difference in this is that both use another mysql class to access database. My whole project is complete and this is last file so I don't want to do the whole work again for a single file. Server logs shows that client denied by server configuration: What should I look for? I have tried the following: Permissions are 644 New file with just simple echo gives 403 too Changed name of folder However, index.php works perfectly. Check the permissions and also ownership of the file. Generally, 403 means

I want to open a file and read its contents as a BufReader using lines() . I also want to be able to seek to the end of the file and write some new lines. Using let mut file lets me write to the file, but once I've given the file to the BufReader I can no longer write to it, as the main function no longer owns file : fn main() { let filename = "tt.txt"; // open a tt.txt file in the local directory let file = OpenOptions::new() .read(true) .write(true) .create(true) .open(filename) .unwrap(); // now read the whole file to get the latest state let date_re = Regex::new(r"^(\d{4})-(\d{2})-(\d{2})"

Considering the following code: fn foo<'a, T: 'a>(t: T) -> Box<Fn() -> &'a T + 'a> { Box::new(move || &t) } What I expect: The type T has lifetime 'a . The value t live as long as T . t moves to the closure, so the closure live as long as t The closure returns a reference to t which was moved to the closure. So the reference is valid as long as the closure exists. There is no lifetime problem, the code compiles. What actually happens: The code does not compile: error[E0495]: cannot infer an appropriate lifetime for borrow expression due to conflicting requirements --> src/lib.rs:2:22 | 2 | Box