zeroshade opened a new pull request, #849:
URL: https://github.com/apache/arrow-go/pull/849
### Rationale for this change
Decimal arrays stringify the raw `decimal.Num` struct instead of the scaled
logical value. `fmt.Println` on a decimal array — or on a
`Record`/`RecordBatch` containing one — prints e.g. `{1999 0}` instead of
`19.99`, even though `ValueStr` already formats the value correctly using the
type's scale. This is inconsistent with `ValueStr`/JSON output and with other
Arrow implementations (e.g. PyArrow prints `19.99`).
### What changes are included in this PR?
- `baseDecimal[T].String()` now formats each non-null value via `ValueStr`
(which applies the type's scale through `GetOneForMarshal`) instead of
`fmt.Sprintf("%v", Value(i))`. Because `baseDecimal` is generic, this corrects
`Decimal32/64/128/256` at once, and `RecordBatch` printing inherits the fix
through the column `String()` path (`record.go`).
- Updated two existing slice-test assertions in `decimal128_test.go` /
`decimal256_test.go` that pinned the old raw-struct output (they were already
inconsistent with the adjacent `ValueStr` expectations on the next lines).
- Added `TestDecimal128StringScaled`, reproducing the issue (`decimal128(5,
2)` = `19.99`) and asserting both the array `String()` and the `RecordBatch`
output.
### Are these changes tested?
Yes. `go test ./arrow/array/` passes, including the new regression test and
the updated slice tests. `go build ./...` and `go vet`/golangci-lint (via
pre-commit) pass.
### Are there any user-facing changes?
Yes — the textual output of `String()` on decimal arrays, and of any
`Record`/`RecordBatch` containing decimal columns, now shows scaled decimal
values (e.g. `19.99`) instead of the internal struct (e.g. `{1999 0}`). This
only affects human-readable stringification; binary/IPC/JSON representations
are unchanged.
Closes #848
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