Rust: Vec<T> extension to move data out of it without copying.

vec_mem_ops.rs

pub trait MemOps {
  fn move_and_clear(&mut self) -> Self;
}

impl<T> MemOps for Vec<T> {
  /// Moves all the elememst of `self` into a new [`Vec`] instance,
  /// leaving `self` empty. **No copying is performed.**
  /// The memory capacity of `self` stays unchanged.
  /// 
  /// # Example
  /// ```
  /// let mut a = vec![1,2,3,4];
  /// let b = a.move_and_clear();
  /// assert_eq!(b.len(), 4);
  /// assert!(a.is_empty());
  /// assert_eq!(a.capacity(), b.capacity());
  /// ```
  fn move_and_clear(&mut self) -> Self {
    let mut new_vec = Vec::with_capacity(self.capacity());
    std::mem::swap(self, &mut new_vec);
    return new_vec;
  }
}

#[cfg(test)]
mod tests {
  use super::*;

  #[test]
  fn test_memops_move_and_clear() {
    let mut a = vec![1,2,3,4];
    let a_ptr_before = a.as_ptr();
    
    let b = a.move_and_clear();
    let a_ptr_after = a.as_ptr();
    let b_ptr_after = b.as_ptr();
    
    assert_ne!(a_ptr_before, a_ptr_after, "Old ptr didn't change");
    assert_eq!(a_ptr_before, b_ptr_after, "Ptr addresses don't match");
    assert_eq!(a.capacity(), b.capacity(), "Capacities don't match");
    assert!(a.is_empty(), "Original vec isn't empty after move");
    assert_eq!(b.len(), 4, "Moved length don't match");
  }
}

vec_usage_example.rs

let mut temp_buffer: Vec<u8> = Vec::new();

// some data is periodically saved to the buffer
// e.g. read from I/O

if temp_buffer.len() >= MINIMAL_DATA_SIZE {
  let data_to_save = temp_buffer.move_and_clear();
  do_some_save(data_to_save)?;
}
  
// temp_buffer is now empty and ready for next data