Method try_insert

src/arrayvec.rs:593–622

(
    &mut self, index: usize, mut item: A::Item,
  )

  /// ```
  #[inline]
  pub fn try_insert(
    &mut self, index: usize, mut item: A::Item,
  ) -> Option<A::Item> {
    assert!(
      index <= self.len as usize,
      "ArrayVec::try_insert> index {} is out of bounds {}",
      index,
      self.len
    );

    // A previous implementation used self.try_push and slice::rotate_right
    // rotate_right and rotate_left generate a huge amount of code and fail to
    // inline; calling them here incurs the cost of all the cases they
    // handle even though we're rotating a usually-small array by a constant
    // 1 offset. This swap-based implementation benchmarks much better for
    // small array lengths in particular.

    if (self.len as usize) < A::CAPACITY {
      self.len += 1;
    } else {
      return Some(item);
    }

    let target = &mut self.as_mut_slice()[index..];
    #[allow(clippy::needless_range_loop)]
    for i in 0..target.len() {
      core::mem::swap(&mut item, &mut target[i]);
    }
    return None;
  }

  /// Checks if the length is 0.
  #[inline(always)]