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https://issues.apache.org/jira/browse/ARROW-16696?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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L. C. Hsieh closed ARROW-16696.
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Resolution: Won't Fix
> [C++] Is Precision check necessary when appending values at decimal builder
> ---------------------------------------------------------------------------
>
> Key: ARROW-16696
> URL: https://issues.apache.org/jira/browse/ARROW-16696
> Project: Apache Arrow
> Issue Type: Improvement
> Reporter: L. C. Hsieh
> Priority: Major
>
> This is one issue found when I'm trying to enable generate_decimal128_case
> integration case for Rust at C++ repo:
> https://github.com/apache/arrow/pull/13219.
> Rust validates precision of decimal in few places, e.g. DecimalBuilder's
> append_value. However, in decimal golden file 0.14.1_decimal.gold.json, there
> are some values failing this check. C++ doesn't perform similar check in
> appending value at decimal builder as I did a search (e.g. Decimal128Builder,
> DecimalFromString), and I can confirm that test case can be passed if I
> remove the check in DecimalBuilder.append_value.
> Actually in C++, similar check is done when doing a full validating
> ArrayData:
> https://github.com/apache/arrow/blob/c715bebbd89089f385c9996560866da23ea1ddda/cpp/src/arrow/array/validate.cc#L672.
> I'm wondering if we should follow C++ at Rust implementation, i.e. removing
> the check from appending value at decimal builder, and moving the check to
> the full validation of ArrayData?
> I opened a Rust PR (https://github.com/apache/arrow-rs/pull/1767) for that.
> Another opinion from the comments is, as we don't do full validation when
> finishing the decimal builder, it seems this check is necessary if it is the
> promise of the builder to always build a valid ArrayData. Then the check is
> needed and it seems C++ needs to add the check there.
> Would like to hear some feedback here. Thanks.
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