[GitHub] [arrow-datafusion] alamb commented on a diff in pull request #6462: Improve `BuiltInFunction` Name Lookup

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

alamb commented on code in PR #6462:
URL: https://github.com/apache/arrow-datafusion/pull/6462#discussion_r1207056961


##########
datafusion/expr/src/built_in_function.rs:
##########
@@ -431,29 +452,21 @@ impl BuiltinScalarFunction {
 
 impl fmt::Display for BuiltinScalarFunction {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        for (func_name, func) in NAME_TO_FUNCTION.iter() {
-            if func == self {
-                return write!(f, "{}", func_name);
-            }
+        if let Some(func_name) = FUNCTION_TO_NAME.get(self) {
+            write!(f, "{}", func_name)
+        } else {
+            // Should not be reached
+            panic!("Internal error: {self:?} not in ALL_FUNCTIONS list");

Review Comment:
   This panic will occur if someone adds a new BuiltInFunction and doesn't add it to the built in list.
   
   I can remove the panic but then if someone doesn't add the function to the new LIST I was worried the error would be masked (the wrong function name would be used or the lookup might fail). But maybe that is preferable 🤔 



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