From a8d9b35d7bcb6fe86c9c625d0d0f2f8777eb1700 Mon Sep 17 00:00:00 2001
From: Sutou Kouhei <kou@clear-code.com>
Date: Fri, 30 Jan 2026 17:10:15 +0900
Subject: [PATCH] GH-49074: [Ruby] Add support for writing interval arrays

---
 .../lib/arrow-format/readable.rb              |  6 +-
 .../red-arrow-format/lib/arrow-format/type.rb | 29 ++++++++
 ruby/red-arrow-format/test/test-writer.rb     | 71 +++++++++++++++++++
 3 files changed, 103 insertions(+), 3 deletions(-)

diff --git a/ruby/red-arrow-format/lib/arrow-format/readable.rb b/ruby/red-arrow-format/lib/arrow-format/readable.rb
index 9cf1beecbebe..867a54c17bdc 100644
--- a/ruby/red-arrow-format/lib/arrow-format/readable.rb
+++ b/ruby/red-arrow-format/lib/arrow-format/readable.rb
@@ -78,11 +78,11 @@ def read_field(fb_field)
       when FB::Interval
         case fb_type.unit
         when FB::IntervalUnit::YEAR_MONTH
-          type = YearMonthIntervalType.new
+          type = YearMonthIntervalType.singleton
         when FB::IntervalUnit::DAY_TIME
-          type = DayTimeIntervalType.new
+          type = DayTimeIntervalType.singleton
         when FB::IntervalUnit::MONTH_DAY_NANO
-          type = MonthDayNanoIntervalType.new
+          type = MonthDayNanoIntervalType.singleton
         end
       when FB::Duration
         unit = fb_type.unit.name.downcase.to_sym
diff --git a/ruby/red-arrow-format/lib/arrow-format/type.rb b/ruby/red-arrow-format/lib/arrow-format/type.rb
index fd7582a7767e..9ba8cae71000 100644
--- a/ruby/red-arrow-format/lib/arrow-format/type.rb
+++ b/ruby/red-arrow-format/lib/arrow-format/type.rb
@@ -458,9 +458,30 @@ def to_flatbuffers
   end
 
   class IntervalType < TemporalType
+    class << self
+      def singleton
+        @singleton ||= new
+      end
+    end
+
+    attr_reader :unit
+    def initialize(unit)
+      super()
+      @unit = unit
+    end
+
+    def to_flatbuffers
+      fb_type = FB::Interval::Data.new
+      fb_type.unit = FB::IntervalUnit.try_convert(@unit.to_s.upcase)
+      fb_type
+    end
   end
 
   class YearMonthIntervalType < IntervalType
+    def initialize
+      super(:year_month)
+    end
+
     def name
       "YearMonthInterval"
     end
@@ -471,6 +492,10 @@ def build_array(size, validity_buffer, values_buffer)
   end
 
   class DayTimeIntervalType < IntervalType
+    def initialize
+      super(:day_time)
+    end
+
     def name
       "DayTimeInterval"
     end
@@ -481,6 +506,10 @@ def build_array(size, validity_buffer, values_buffer)
   end
 
   class MonthDayNanoIntervalType < IntervalType
+    def initialize
+      super(:month_day_nano)
+    end
+
     def name
       "MonthDayNanoInterval"
     end
diff --git a/ruby/red-arrow-format/test/test-writer.rb b/ruby/red-arrow-format/test/test-writer.rb
index c440bc4a597a..841194ff51d9 100644
--- a/ruby/red-arrow-format/test/test-writer.rb
+++ b/ruby/red-arrow-format/test/test-writer.rb
@@ -61,6 +61,12 @@ def convert_type(red_arrow_type)
     when Arrow::TimestampDataType
       ArrowFormat::TimestampType.new(convert_time_unit(red_arrow_type.unit),
                                      red_arrow_type.time_zone&.identifier)
+    when Arrow::MonthIntervalDataType
+      ArrowFormat::YearMonthIntervalType.singleton
+    when Arrow::DayTimeIntervalDataType
+      ArrowFormat::DayTimeIntervalType.singleton
+    when Arrow::MonthDayNanoIntervalDataType
+      ArrowFormat::MonthDayNanoIntervalType.singleton
     when Arrow::BinaryDataType
       ArrowFormat::BinaryType.singleton
     when Arrow::LargeBinaryDataType
@@ -523,6 +529,71 @@ def test_type
           end
         end
 
+        sub_test_case("YearMonthInterval") do
+          def build_array
+            Arrow::MonthIntervalArray.new([0, nil, 100])
+          end
+
+          def test_write
+            assert_equal([0, nil, 100],
+                         @values)
+          end
+        end
+
+        sub_test_case("DayTimeInterval") do
+          def build_array
+            Arrow::DayTimeIntervalArray.new([
+                                              {day: 1, millisecond: 100},
+                                              nil,
+                                              {day: 3, millisecond: 300},
+                                            ])
+          end
+
+          def test_write
+            assert_equal([
+                           {day: 1, millisecond: 100},
+                           nil,
+                           {day: 3, millisecond: 300},
+                         ],
+                         @values)
+          end
+        end
+
+        sub_test_case("MonthDayNanoInterval") do
+          def build_array
+            Arrow::MonthDayNanoIntervalArray.new([
+                                                   {
+                                                     month: 1,
+                                                     day: 1,
+                                                     nanosecond: 100,
+                                                   },
+                                                   nil,
+                                                   {
+                                                     month: 3,
+                                                     day: 3,
+                                                     nanosecond: 300,
+                                                   },
+                                                 ])
+          end
+
+          def test_write
+            assert_equal([
+                           {
+                             month: 1,
+                             day: 1,
+                             nanosecond: 100,
+                           },
+                           nil,
+                           {
+                             month: 3,
+                             day: 3,
+                             nanosecond: 300,
+                           },
+                         ],
+                         @values)
+          end
+        end
+
         sub_test_case("Binary") do
           def build_array
             Arrow::BinaryArray.new(["Hello".b, nil, "World".b])