hcrosse opened a new issue, #1489:
URL: https://github.com/apache/arrow-go/issues/1489
### Describe the bug, including details regarding any error messages,
version, and platform.
`arrow/scalar` has no scalar types for `string_view` or `binary_view`.
`GetScalar` returns an error for a valid value but panics on a null slot.
`Dictionary.GetEncodedValue` on a null dictionary scalar with view values also
panics. Casting a null string scalar to `string_view` through
`compute.CastDatum` panics in an executor goroutine and crashes the process.
I reproduced these on main at `66722e30`, on macOS arm64 with Go 1.26.10.
The three null cases also reproduce on v18.8.0.
**Reproduction**
Save this as `main.go` in a new subdirectory of an arrow-go checkout at
`66722e30df98ddd6f7bb46023fa13287b84308f6`, then run `go run . valid`, `go run
. getscalar`, `go run . encoded` and `go run . cast` from that directory:
```go
package main
import (
"context"
"fmt"
"os"
"github.com/apache/arrow-go/v18/arrow"
"github.com/apache/arrow-go/v18/arrow/array"
"github.com/apache/arrow-go/v18/arrow/compute"
"github.com/apache/arrow-go/v18/arrow/memory"
"github.com/apache/arrow-go/v18/arrow/scalar"
)
func main() {
sv := arrow.BinaryTypes.StringView
switch os.Args[1] {
case "valid":
b := array.NewStringViewBuilder(memory.DefaultAllocator)
b.Append("hello")
fmt.Println(scalar.GetScalar(b.NewArray(), 0))
case "getscalar":
arr := array.MakeArrayOfNull(memory.DefaultAllocator, sv, 1)
fmt.Println(scalar.GetScalar(arr, 0))
case "encoded":
dict :=
scalar.NewNullDictScalar(&arrow.DictionaryType{IndexType:
arrow.PrimitiveTypes.Int8, ValueType: sv})
fmt.Println(dict.GetEncodedValue())
case "cast":
fmt.Println(compute.CastDatum(context.Background(),
compute.NewDatum(scalar.MakeNullScalar(arrow.BinaryTypes.String)),
compute.SafeCastOptions(sv)))
}
}
```
| Command | Main | Expected |
| --- | --- | --- |
| `valid` | `<nil> cannot create scalar from array of type string_view` |
`hello <nil>` |
| `getscalar`, `encoded`, `cast` | nil pointer panic | `null <nil>` |
**Cause**
`GetScalar` has no view cases, and the null constructor table has nil
entries for both types. `MakeNullScalar` calls those entries:
https://github.com/apache/arrow-go/blob/66722e30df98ddd6f7bb46023fa13287b84308f6/arrow/scalar/scalar.go#L489-L491
https://github.com/apache/arrow-go/blob/66722e30df98ddd6f7bb46023fa13287b84308f6/arrow/scalar/scalar.go#L586-L588
https://github.com/apache/arrow-go/blob/66722e30df98ddd6f7bb46023fa13287b84308f6/arrow/scalar/nested.go#L519-L521
C++ has
[`StringViewScalar`](https://github.com/apache/arrow/blob/1ebb9379b2f635755e773b79e88cb99852c70455/cpp/src/arrow/scalar.h#L392-L403)
and
[`BinaryViewScalar`](https://github.com/apache/arrow/blob/1ebb9379b2f635755e773b79e88cb99852c70455/cpp/src/arrow/scalar.h#L355-L390).
The Go gap is noted in https://github.com/apache/arrow-go/pull/802 and
https://github.com/apache/arrow-go/pull/1448.
I have a patch with tests and can open a PR.
### Component(s)
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