Always consider the time and space complexity implications of your code. Choose data structures and algorithms that minimize computational overhead and memory usage for your specific use cases. **Watch for hidden complexity issues:** 1. **Avoid nested iterations that create O(n²) behavior** ```rust // Poor: Iterates through all buffers on each call, potentially O(n²) in a loop let n = bufs.iter().map(|b| b.len()).sum::().min(MAX_BUF); // Better: Calculate incrementally inside a loop to maintain O(n) complexity let mut remaining = MAX_BUF; let mut total = 0; for buf in bufs { let to_copy = buf.len().min(remaining); total += to_copy; remaining -= to_copy; if remaining == 0 { break; } } ``` 2. **Choose efficient operations over expensive ones** ```rust // Poor: Using power operation which is more expensive let max_number = 2u64.saturating_pow((8 * length_field_len - 1) as u32); // Better: Using bit shift which is much faster let max_number = match 1.checked_shl(8 * length_field_len) { Some(shl) => shl - 1, None => u64::MAX, }; ``` 3. **Design for fairness when consuming from multiple sources** ```rust // When polling multiple streams, implement rotation strategies to ensure // fair processing and prevent starvation: let mut added = 0; let mut start = thread_rng_n(entries.len() as u32) as usize; while added < limit { match self.poll_one(cx, start) { Poll::Ready(Some((idx, val))) => { added += 1; // Move the start index to ensure fair rotation start = idx.wrapping_add(1) % entries.len(); // Process val... } _ => break, } } ``` 4. **Use iterators over index-based access when appropriate** ```rust // Poor: Using index-based access in a loop let expiration_time = (0..wheel_count) .filter_map(|id| wheel.get_sharded_wheel_mut(id).next_expiration_time()) .min(); // Better: Using iterator methods directly on the collection let expiration_time = wheels.iter_mut() .filter_map(|wheel| wheel.next_expiration_time()) .min(); ``` 5. **Avoid code duplication that leads to excessive monomorphization** ```rust // Poor: Duplicating implementation for each function call type pub fn with_func1(cmd: &mut Cmd, with: impl Fn(&mut Cmd) -> Result) -> Result { // Duplicated implementation } // Better: Extract common logic to avoid recompiling the same code pub fn with_func(cmd: &mut Cmd, with: impl Fn(&mut Cmd) -> Result) -> Result { handle_common(&mut with(cmd)?) } fn handle_common(child: &mut Child) -> Result { // Common implementation that won't be duplicated } ``` By paying attention to these efficiency concerns, you'll produce code that scales better and uses resources more efficiently.