Fokko commented on code in PR #36846:
URL: https://github.com/apache/arrow/pull/36846#discussion_r1307101413
##########
cpp/src/arrow/type.h:
##########
@@ -397,14 +397,67 @@ class ARROW_EXPORT Field : public detail::Fingerprintable,
/// \brief Options that control the behavior of `MergeWith`.
/// Options are to be added to allow type conversions, including integer
/// widening, promotion from integer to float, or conversion to or from
boolean.
- struct MergeOptions {
+ struct ARROW_EXPORT MergeOptions : public
util::ToStringOstreamable<MergeOptions> {
/// If true, a Field of NullType can be unified with a Field of another
type.
/// The unified field will be of the other type and become nullable.
/// Nullability will be promoted to the looser option (nullable if one is
not
/// nullable).
bool promote_nullability = true;
+ /// Allow a decimal to be unified with another decimal of the same
+ /// width, adjusting scale and precision as appropriate. May fail
+ /// if the adjustment is not possible.
+ bool promote_decimal = false;
+
+ /// Allow a decimal to be promoted to a float. The float type will
+ /// not itself be promoted (e.g. Decimal128 + Float32 = Float32).
+ bool promote_decimal_to_float = false;
+
+ /// Allow an integer to be promoted to a decimal.
+ ///
+ /// May fail if the decimal has insufficient precision to
+ /// accommodate the integer. (See increase_decimal_precision.)
+ bool promote_integer_to_decimal = false;
+
+ /// Allow an integer of a given bit width to be promoted to a
+ /// float; the result will be a float of an equal or greater bit
+ /// width to both of the inputs.
+ bool promote_integer_to_float = false;
Review Comment:
Updated the docstring to:
```
/// Allow an integer of a given bit width to be promoted to a
/// float; the result will be a float of an equal or greater bit
/// width to both of the inputs. Examples:
/// - int8 + float32 = float32
/// - int32 + float32 = float64
/// - int32 + float64 = float64
/// Because an int32 cannot always be represented exactly in the
/// 24 bits of a float32 mantissa.
```
Let me know if you had an other place in mind to document this.
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