Nathan-Fenner opened a new pull request, #5086:
URL: https://github.com/apache/arrow-rs/pull/5086
# Which issue does this PR close?
Closes #5011.
# Rationale for this change
The arrow compute kernel function `zip` can now work on scalars, allowing a
scalar value to be "zipped" with another array, repeating the scalar where
needed to fill in the selected spots:
<table>
<thead>
<tr>
<td><b>Before</b></td><td><b>After</b></td>
</tr>
</thead>
<tbody>
<tr>
<td>
<pre>
pub fn zip(
mask: &BooleanArray,
truthy: &dyn Array,
falsy: &dyn Array,
) -> Result<ArrayRef, ArrowError> { ... }
</pre>
</td>
<td>
<pre>
pub fn zip(
mask: &BooleanArray,
truthy: impl Datum,
falsy: impl Datum,
) -> Result<ArrayRef, ArrowError> { ... }
</pre>
</td>
</tr>
</tbody>
</table>
If a `Scalar` value is provided, then it will be copied to fill every spot
specified in the `mask`. Previously, callers would be required to implement
this logic internally to support this.
Since `&dyn Array` already implements `Datum`, existing calls will still
continue to work exactly as they did before, but it is now also possible to
pass in a scalar value.
In addition, `&dyn Datum` now implements `Datum`. This means that `zip` can
be called with the same signature as e.g. `add`, which explicitly ask for `&dyn
Datum`; otherwise, it would not be possible to call `zip` with the same kind of
signature as `add`.
(I think in a future PR, it would be a good idea to change `add`, `sub`, and
all of the other computing kernels to take `impl Datum` parameters instead of
`&dyn Datum` parameters for maximum flexibility and efficiency)
# What changes are included in this PR?
- `zip`'s signature changes from `&dyn Array` to `impl Datum`
- `&dyn Datum` now implements `Datum`
# Are there any user-facing changes?
- `zip` now supports `Scalar`/`Datum` arguments
- `&dyn Datum` now implements `Datum`
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