[PR] Implement Ord for DataType [arrow-rs]

["ch-sc (via GitHub)" <gi...@apache.org>]

ch-sc opened a new pull request, #4920:
URL: https://github.com/apache/arrow-rs/pull/4920

   # Which issue does this PR close?
   
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   Closes #4919 (Compare `DataType` based on memory size).
   
   # Rationale for this change
    
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   # What changes are included in this PR?
   
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   # Are there any user-facing changes?
   
   These changes will alter the way `DataType` is ordered. Users who rely on the current ordering, which is just the basic derived implementation for `Ord`, might be affected.
   
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Re: [PR] Implement Ord for DataType [arrow-rs]

["ch-sc (via GitHub)" <gi...@apache.org>]

ch-sc closed pull request #4920: Implement Ord for DataType
URL: https://github.com/apache/arrow-rs/pull/4920


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Re: [PR] Implement Ord for DataType [arrow-rs]

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

tustvold commented on code in PR #4920:
URL: https://github.com/apache/arrow-rs/pull/4920#discussion_r1355107483


##########
arrow-schema/src/datatype.rs:
##########
@@ -310,6 +311,38 @@ impl fmt::Display for DataType {
     }
 }
 
+impl PartialOrd for DataType {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Ord for DataType {
+    fn cmp(&self, other: &Self) -> Ordering {
+        match (self, other) {
+            (DataType::Null, DataType::Null) => Ordering::Equal,
+            (DataType::Null, _) => Ordering::Less,
+            (_, DataType::Null) => Ordering::Greater,
+            (DataType::Boolean, DataType::Boolean) => Ordering::Equal,
+            (DataType::Boolean, _) => Ordering::Less,
+            (_, DataType::Boolean) => Ordering::Greater,
+            (a, b) => {
+                if a.is_primitive() && b.is_primitive() {
+                    self.primitive_width()
+                        .unwrap_or(0)
+                        .cmp(&other.primitive_width().unwrap_or(0))

Review Comment:
   This is inconsistent with the implementation of Eq and is therefore ill-formed



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Re: [PR] Implement Ord for DataType [arrow-rs]

["ch-sc (via GitHub)" <gi...@apache.org>]

ch-sc commented on PR #4920:
URL: https://github.com/apache/arrow-rs/pull/4920#issuecomment-1757935069

   Thanks for your feedback @tustvold. I'll do it in DataFusion


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