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Add downcast macros (#2635) #2636

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merged 3 commits into from Sep 2, 2022
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tustvold
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@tustvold tustvold commented Sep 2, 2022

Which issue does this PR close?

Closes #2635

Rationale for this change

I find myself frequently writing the same code, we can instead generate this with macros. This will also benefit downstreams and acts to reduce the current situation where we have ergonomic but limited dyn-dispatch, or significantly more verbose manual-dispatch but with full flexibility.

What changes are included in this PR?

Adds two macros downcast_primitive and downcast_dict.

Are there any user-facing changes?

@github-actions github-actions bot added the arrow Changes to the arrow crate label Sep 2, 2022
@@ -358,92 +336,12 @@ fn filter_array(values: &dyn Array, predicate: &FilterPredicate) -> Result<Array
IterationStrategy::None => Ok(new_empty_array(values.data_type())),
IterationStrategy::All => Ok(make_array(values.data().slice(0, predicate.count))),
// actually filter
_ => match values.data_type() {
_ => downcast_primitive_array! {
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@tustvold tustvold Sep 2, 2022

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Unfortunately rust doesn't support macros in branch position, and so this was the best I could come up with - rust-lang/rfcs#2654

>($values);
$e
}
$crate::datatypes::DataType::Float16 => {
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This was actually missing before

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@alamb alamb left a comment

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I think it looks great, personally. Only one small suggestion

/// # use arrow::array::as_string_array;
///
/// fn print_primitive(array: &dyn Array) {
/// downcast_primitive_array!(
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❤️ that certainly will make the macros in code such as https://github.com/apache/arrow-datafusion/blob/master/datafusion/physical-expr/src/expressions/binary.rs easier to deal with ❤️

/// println!("{:?}", v);
/// }
/// }
/// t => println!("Unsupported datatype {}", t)
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I think it would be good to extend this example to show the String array as well -- not only to document how to support other types, but also because the StringArray is so common

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Done, and threw in a bit of TypedDictionaryArray spice as well 😆

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🥘 👍

@@ -358,92 +336,12 @@ fn filter_array(values: &dyn Array, predicate: &FilterPredicate) -> Result<Array
IterationStrategy::None => Ok(new_empty_array(values.data_type())),
IterationStrategy::All => Ok(make_array(values.data().slice(0, predicate.count))),
// actually filter
_ => match values.data_type() {
_ => downcast_primitive_array! {
values => Ok(Arc::new(filter_primitive(values, predicate))),
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👨‍🍳 👌

Very nice

@tustvold tustvold merged commit 5a49cfe into apache:master Sep 2, 2022
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ursabot commented Sep 2, 2022

Benchmark runs are scheduled for baseline = 2d3a350 and contender = 5a49cfe. 5a49cfe is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ec2-t3-xlarge-us-east-2] ec2-t3-xlarge-us-east-2
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on test-mac-arm] test-mac-arm
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ursa-i9-9960x] ursa-i9-9960x
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ursa-thinkcentre-m75q] ursa-thinkcentre-m75q
Buildkite builds:
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java

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Add Macros to assist with static dispatch
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