mqy commented on a change in pull request #9122:
URL: https://github.com/apache/arrow/pull/9122#discussion_r553426212
##########
File path: rust/arrow/src/array/array_struct.rs
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@@ -69,6 +69,9 @@ impl StructArray {
}
/// Return child array whose field name equals to column_name
+ ///
+ /// Note: The Arrow specification allows for duplicate field names, and in
such
Review comment:
From the IPC doc: `A struct is a nested type parameterized by an ordered
sequence of types (which can all be distinct), called its fields. Each field
must have a UTF8-encoded name, and these field names are part of the type
metadata.`
The `which can all be distinct` is totally wasting of time, isn't it?
From C++:
https://github.com/apache/arrow/blob/57376d28cf433bed95f19fa44c1e90a780ba54e8/cpp/src/arrow/type.cc
```c++
// From this point, there's one or more field in the builder that exists
with
// the same name.
if (policy_ == CONFLICT_IGNORE) {
// The ignore policy is more generous when there's duplicate in the
builder.
return Status::OK();
} else if (policy_ == CONFLICT_ERROR) {
return Status::Invalid("Duplicate found, policy dictate to treat as an
error");
}
```
From java
https://github.com/apache/arrow/blob/25c736d48dc289f457e74d15d05db65f6d539447/java/vector/src/main/java/org/apache/arrow/vector/complex/AbstractStructVector.java
```java
/**
* Policy to determine how to react when duplicate columns are encountered.
*/
public enum ConflictPolicy {
// Ignore the conflict and append the field. This is the default
behaviour
CONFLICT_APPEND,
// Keep the existing field and ignore the newer one.
CONFLICT_IGNORE,
// Replace the existing field with the newer one.
CONFLICT_REPLACE,
// Refuse the new field and error out.
CONFLICT_ERROR
}
```
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