Efficiently mutate a vector while also iterating over the same vector

by

The simplest way is to just use indices, which don’t involve any long-lived borrows:

for i in 0..v.len() {
    for j in 0..v.len() {
        if i == j { continue; }
        if v[j].a > v[i].a {
            v[i].a += 1;
        }
    }
}

If you really, really want to use iterators, you can do it by dividing up the Vec into disjoint slices:

fn process(elem: &mut MyStruct, other: &MyStruct) {
    if other.a > elem.a {
        elem.a += 1;
    }
}

for i in 0..v.len() {
    let (left, mid_right) = v.split_at_mut(i);
    let (mid, right) = mid_right.split_at_mut(1);
    let elem = &mut mid[0];

    for other in left {
        process(elem, other);
    }
    for other in right {
        process(elem, other);
    }
}

More Related Contents:

  1. Why can’t I store a value and a reference to that value in the same struct?
  2. How do I create a heterogeneous collection of objects?
  3. Is it possible to control the size of an array using the type parameter of a generic?
  4. How do I stop iteration and return an error when Iterator::map returns a Result::Err?
  5. Are polymorphic variables allowed?
  6. Does println! borrow or own the variable?
  7. Why does Iterator::take_while take ownership of the iterator?
  8. When should I implement std::convert::From vs std::convert::Into?
  9. Why would I implement methods on a trait instead of as part of the trait?
  10. “Expected fn item, found a different fn item” when working with function pointers
  11. How do you unwrap a Result on Ok or return from the function on Err?
  12. What does “mismatched types: expected `()`” mean when using an if expression?
  13. How do I read the entire body of a Tokio-based Hyper request?
  14. When returning the outcome of consuming a StdinLock, why was the borrow to stdin retained?
  15. How does Rust pattern matching determine if the bound variable will be a reference or a value?
  16. Using generic trait methods like .into() when type inference is impossible
  17. Why does an enum require extra memory size?
  18. Why does Rust disallow mutable aliasing?
  19. How to store rusqlite Connection and Statement objects in the same struct in Rust? [duplicate]
  20. Why can’t I reuse a &mut reference after passing it to a function that accepts a generic type?
  21. print! macro not executed until pressing Enter
  22. How can I define an async method in a trait?
  23. How can I override a constant via a compiler option?
  24. Why am I getting “parameter is never used [E0392]”?
  25. Why is Rust’s assert_eq! implemented using a match?
  26. Is there a list of all cfg features?
  27. Comparing every element in a vector with the next one
  28. Is there a good way to convert a Vec to an array?
  29. How can I conditionally provide a default reference without performing unnecessary computation when it isn’t used?
  30. How can I build multiple binaries with Cargo?

Leave a Comment