tustvold commented on code in PR #5460:
URL: https://github.com/apache/arrow-rs/pull/5460#discussion_r1510351055
##########
arrow-buffer/src/buffer/immutable.rs:
##########
@@ -423,24 +423,11 @@ impl Buffer {
impl<T: ArrowNativeType> FromIterator<T> for Buffer {
fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
- let mut iterator = iter.into_iter();
+ //let mut iterator = iter.into_iter();
let size = std::mem::size_of::<T>();
-
- // first iteration, which will likely reserve sufficient space for the
buffer.
- let mut buffer = match iterator.next() {
- None => MutableBuffer::new(0),
- Some(element) => {
- let (lower, _) = iterator.size_hint();
- let mut buffer =
MutableBuffer::new(lower.saturating_add(1).saturating_mul(size));
- unsafe {
- std::ptr::write(buffer.as_mut_ptr() as *mut T, element);
- buffer.set_len(size);
- }
- buffer
- }
- };
-
- buffer.extend_from_iter(iterator);
+ let vec = Vec::from_iter(iter);
Review Comment:
This method will now copy the data twice
##########
arrow-buffer/src/buffer/immutable.rs:
##########
@@ -423,24 +423,11 @@ impl Buffer {
impl<T: ArrowNativeType> FromIterator<T> for Buffer {
fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
- let mut iterator = iter.into_iter();
+ //let mut iterator = iter.into_iter();
let size = std::mem::size_of::<T>();
-
- // first iteration, which will likely reserve sufficient space for the
buffer.
- let mut buffer = match iterator.next() {
- None => MutableBuffer::new(0),
- Some(element) => {
- let (lower, _) = iterator.size_hint();
- let mut buffer =
MutableBuffer::new(lower.saturating_add(1).saturating_mul(size));
- unsafe {
- std::ptr::write(buffer.as_mut_ptr() as *mut T, element);
- buffer.set_len(size);
- }
- buffer
- }
- };
-
- buffer.extend_from_iter(iterator);
+ let vec = Vec::from_iter(iter);
+ let mut buffer = MutableBuffer::new(vec.len() * size);
Review Comment:
You could use Buffer::from_vec here to avoid a copy
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