[GitHub] [arrow] bkietz commented on a diff in pull request #14241: ARROW-17846: [C++] Use `if constexpr` in CSV subsystem

[GitBox <gi...@apache.org>]

bkietz commented on code in PR #14241:
URL: https://github.com/apache/arrow/pull/14241#discussion_r980445728


##########
cpp/src/arrow/visit_type_inline.h:
##########
@@ -57,6 +57,33 @@ inline Status VisitTypeInline(const DataType& type, VISITOR* visitor) {
 
 #undef TYPE_VISIT_INLINE
 
+#define TYPE_VISIT_INLINE(TYPE_CLASS)      \
+  case TYPE_CLASS##Type::type_id:          \
+    return std::forward<VISITOR>(visitor)( \
+        internal::checked_cast<const TYPE_CLASS##Type&>(type));
+
+/// \brief Call `visitor` with the corresponding concrete type class
+///
+/// Unlike VisitTypeInline which calls `visitor.Visit`, here `visitor`
+/// itself is called.
+/// `visitor` must support a `const DataType&` argument as a fallback,
+/// in addition to concrete type classes.
+///
+/// The intent is for this to be called on a generic lambda
+/// that may internally use `if constexpr` or similar constructs.
+template <typename VISITOR>
+inline auto VisitType(const DataType& type, VISITOR&& visitor)

Review Comment:
   LGTM



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