jhorstmann opened a new pull request, #10172:
URL: https://github.com/apache/arrow-rs/pull/10172
# Which issue does this PR close?
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- Closes #10164.
# Rationale for this change
The `FromBitpacked` trait was introduced in #9662 as a marker for types that
could be decoded from bitpacked data, but the implementation still mostly used
methods from its `FromBytes` super-trait. The implementation of
`BitReader::get_batch` that dispatched on the size of the type then required a
complex safety contract, which meant that `FromBytes` had to be an `unsafe`
trait.
Instead of that size dispatch, we can move the unsafe code into a method of
the `FromBitpacked` trait, which makes `BitReader::get_batch` completely safe.
This also removes the need to make any of those traits sealed as proposed in
#10166.
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# What changes are included in this PR?
The responsibilities of the `FromBytes` and `FromBitpacked` traits should be
much clearer now:
- `FromBytes` is used for plain encoded data
- `FromBitpacked` is used for bitpacked data
Unsafe code is moved from `BitReader::get_batch` into some of the
`FromBitpacked` implementations.
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# Are these changes tested?
All existing tests pass.
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# Are there any user-facing changes?
`FromBitpacked` gains a new method and is no longer a sub-trait of
`FromBytes`, so this might be breaking change. Code that previously implemented
`FromBytes` will need to change to remove the `unsafe` keyword and
`BIT_CAPACITY` constant.
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