thorfour opened a new pull request, #36759:
URL: https://github.com/apache/arrow/pull/36759
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### Rationale for this change
The hashing.MemoTable provides an interface with
```go
GetOrInsert(val interface{}) (idx int, existed bool, err error)
```
This can cause a costly allocation for binary dictionaries as is detailed in
issue #36671
Instead we can change the `BinaryDictionaryBuilder` to use a different type
of builder that uses a memotable that allows the static `[]byte` type as part
of the `GetOrInsert` function to prevent that allocation when converting from
`[]byte` to `interface{}`.
Originally I attempted to replace the memotable with a generic `MemoTable[T
any]` but because there are two different implementations of memo tables one
being for binary memo tables, I tried splitting the generic implementations in
two. That code can bee seen on [this
branch](https://github.com/thorfour/arrow/tree/go-generic-memotable). This runs
into the problem that the util function attempts to convert the memo table back
into its implementation:
https://github.com/apache/arrow/blob/de8df23a8cd9737b4df5bb1b68fc12a54f252d0d/go/arrow/array/util.go#L268
which Go doesn't allow due to the generic binary memo table being more
restrictive than the basic one. So to move forward with replacing the memotable
with generics I believe we would need a single implementation of the memo table
but would also require things like the builders to be generic as well.
### What changes are included in this PR?
Adds a `binaryDictionaryBuilder` that is a identical copy to the
`dictionaryBuilder` except is uses `[]byte` instead of `interface{}`
For binary dictionary types it now uses the the `binaryDictionaryBuilder`
type to avoid the conversion of `[]byte` to `interface{}`
### Are these changes tested?
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No additional tests have been added for this yet, current test coverage
exercises the new builders. But wanted to ensure this was a valid path forward
before investing more time in test coverage if deemed necessary.
### Are there any user-facing changes?
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