huan233usc commented on code in PR #793:
URL: https://github.com/apache/iceberg-cpp/pull/793#discussion_r3522002561
##########
src/iceberg/update/update_schema.cc:
##########
@@ -282,6 +289,34 @@ std::vector<SchemaField> ApplyChangesVisitor::MoveFields(
return reordered;
}
+/// \brief Cast a default value literal to a target primitive type.
+///
+/// `Literal::CastTo` only returns a value for identical decimal types, but
schema
+/// evolution permits widening a decimal to a larger precision at the SAME
scale. Such a
+/// promotion leaves the unscaled value unchanged, so the literal is rebuilt
with the
+/// target type instead of going through `CastTo`. A scale change is NOT
handled here: the
+/// unscaled value only keeps its meaning at the same scale (a decimal default
must match
+/// the column scale), so differing scales fall through to `CastTo` and are
rejected. All
+/// other conversions delegate to `CastTo`, which reports narrowing via
AboveMax/BelowMin
+/// sentinels that callers reject.
+///
+/// \pre `target_type` is non-null; every caller passes a resolved field type.
`value` is
+/// the caller's dereferenced default, so a missing default must be filtered
out before
+/// this is reached.
+Result<Literal> CastDefaultToType(const Literal& value,
+ const std::shared_ptr<PrimitiveType>&
target_type) {
+ if (value.type()->type_id() == TypeId::kDecimal &&
+ target_type->type_id() == TypeId::kDecimal) {
+ const auto& source_type = internal::checked_cast<const
DecimalType&>(*value.type());
+ const auto& decimal_type = internal::checked_cast<const
DecimalType&>(*target_type);
+ if (source_type.scale() == decimal_type.scale()) {
+ return Literal::Decimal(std::get<Decimal>(value.value()).value(),
+ decimal_type.precision(), decimal_type.scale());
+ }
+ }
+ return value.CastTo(target_type);
Review Comment:
Filed as #805, which adds int/long/float/double → decimal casts in
`Literal::CastTo` (float/double use HALF_UP rounding to match Java). Keeping it
out of this PR to stay scoped to the evolution change.
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