bkietz commented on a change in pull request #10016:
URL: https://github.com/apache/arrow/pull/10016#discussion_r614139893
##########
File path: cpp/src/arrow/compute/kernels/scalar_arithmetic.cc
##########
@@ -309,6 +348,21 @@ std::shared_ptr<ScalarFunction>
MakeArithmeticFunctionNotNull(std::string name,
return func;
}
Review comment:
`ScalarFunction` does not provide implicit casts, such as from unsigned
to signed integers. `UnaryScalarFunction` is provided to add implicit casts
including:
```
uint8 -> int16
uint16 -> int32
uint32 -> int64
uint64 -> int64
dictionary<int32, float> -> float
//...
```
The call to CommonNumeric with int8 ensures that the output type is signed,
with no more widening than necessary. Insertion of implicit casts is tested for
the other arithmetic functions using
[CheckDispatchBest](https://github.com/apache/arrow/blob/b4806a0eefb5b21e9f44cac1c7c9113a4c31ad01/cpp/src/arrow/compute/kernels/scalar_arithmetic_test.cc#L645)
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