[GitHub] [arrow-rs] waynexia commented on a diff in pull request #3783: Return Buffers from ArrayData::buffers instead of slice (#1799)

["waynexia (via GitHub)" <gi...@apache.org>]

waynexia commented on code in PR #3783:
URL: https://github.com/apache/arrow-rs/pull/3783#discussion_r1122572534


##########
arrow-data/src/data/buffers.rs:
##########
@@ -0,0 +1,97 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use arrow_buffer::Buffer;
+use std::iter::Chain;
+use std::ops::Index;
+
+/// A collection of [`Buffer`]
+#[derive(Debug, Default, Copy, Clone, Eq, PartialEq)]
+pub struct Buffers<'a>([Option<&'a Buffer>; 2]);
+
+impl<'a> Buffers<'a> {
+    /// Temporary will be removed once ArrayData does not store `Vec<Buffer>` directly (#3769)
+    #[inline]
+    pub(crate) fn from_slice(a: &'a [Buffer]) -> Self {
+        match a.len() {
+            0 => Self([None, None]),
+            1 => Self([Some(&a[0]), None]),
+            _ => Self([Some(&a[0]), Some(&a[1])]),
+        }
+    }
+
+    /// Returns the number of [`Buffer`] in this collection
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.0[0].is_some() as usize + self.0[1].is_some() as usize
+    }
+
+    /// Returns `true` if this collection is empty
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.0[0].is_none() && self.0[1].is_none()
+    }
+
+    #[inline]
+    pub fn iter(&self) -> IntoIter<'a> {
+        self.into_iter()
+    }
+
+    /// Converts this [`Buffers`] to a `Vec<Buffer>`
+    #[inline]
+    pub fn to_vec(&self) -> Vec<Buffer> {
+        self.iter().cloned().collect()
+    }
+}
+
+impl<'a> Index<usize> for Buffers<'a> {
+    type Output = &'a Buffer;
+
+    #[inline]
+    fn index(&self, index: usize) -> &Self::Output {

Review Comment:
   I tried changing it to `type Output = Buffer` and got tons of errors. The one you mentioned can be fixed by introducing a temp variable for `array.data().buffers()` (very verbose...). But I don't know how to fix it if something else references `buffer`...
   
   So I'm ok with `&&Buffer` here. Not sure if it's the only way but it does make other things easier (to me).



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