Rust vec drain let mut vec = vec!['a', 'b', 'c']; let mut drain = vec. For now we'll only implement the "basic" full-range version. Keep unyielded elements in the source Vec. drain(. collect() returns the correct value for drained but empties the whole vector. Not in stable Rust 1. What is a drain method on iterator used for? It is used to remove a range of elements from a vector, optionally giving you the elements in the range. Drain is largely the same as IntoIter, except that instead of consuming the Vec, it borrows the Vec and leaves its allocation untouched. keep_rest(); // If we wouldn't call `keep_rest()`, // `vec` would be v. ); assert_eq!(drain. Playground. This struct is created by Vec::drain. collect(); Drain. I want to remove first N (0 <<< N < length) elements in Vec. drain. drain_filter(|&mut e| e % 2 == 0). Specialization does wonders here. There's an unstable nightly feature called drain_filter that does exactly what you want: let mut v: Vec<i32> = vec![1, 2, 3, 4, 5, 6]; let drained: Vec<i32> = v. Why clear couldn't be used? Clear removes all values in the vector, but drain lets you remove only a sub-range. Implementations impl<'a, T> Drain<'a, T> pub fn as_slice(&self) -> &[T] ⓘ Keep unyielded elements in the source Vec. ). This struct is created by the drain method on Vec. Let's move on to Drain. filter(condition). This means that you can insert new elements in the Vec without having to allocate storage for them until you reach the Vec's capacity. 33. If we drop the O (1) space, we build a new vector, then copy it back. 0. From the duplicate: After using drain, the Vec is empty but the storage previously allocated for its elements remains allocated. unwrap(), 'a'); // This call keeps 'b' and 'c' in the vec. Implementations impl<'a, T> Drain<'a, T> pub fn as_slice(&self) -> &[T] ⓘ. . However, removing many elements using Vec::drain is quite slow (190x slower than ptr::copy). Struct std::vec::Drain pub struct Drain<'a, T> where T: 'a, { /* fields omitted */ } A draining iterator for Vec<T>. The solution is to use Vec::drain. It's actually possible to have O (1) space with into_iter + filter_map + collect. A draining iterator for Vec<T>. I've already found a solution here. Struct std:: vec:: Drain Unstable pub struct Drain<'a, T> where T: 'a { // some fields omitted } It's simpler to do this using unsafe code that leaves a gap of uninitialized memory during the process, just as drain_filter does. next(). cloqj vzds dsnqfwed rqv gufosen bexk fcdnlmt mjw euxj dymcjxb