From c71fd12f82ad3e5e87b59c6adede0cdf113c622c Mon Sep 17 00:00:00 2001
From: John W Higgins <wishdev@gmail.com>
Date: Tue, 1 Jul 2025 19:45:59 -0700
Subject: [PATCH 1/4] Increase speed of Table#to_csv when encoding is provided

If we set the encoding when we call Table#to_csv we do not need
to go row by row to determine the encoding to use. This allows
the use of CSV#generate_lines as a faster exporter.
---
 lib/csv/table.rb       | 11 ++++++++---
 test/csv/test_table.rb |  9 +++++++++
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/lib/csv/table.rb b/lib/csv/table.rb
index fb19f545..66a2d596 100644
--- a/lib/csv/table.rb
+++ b/lib/csv/table.rb
@@ -1006,10 +1006,15 @@ def to_csv(write_headers: true, limit: nil, **options)
       limit ||= @table.size
       limit = @table.size + 1 + limit if limit < 0
       limit = 0 if limit < 0
-      @table.first(limit).each do |row|
-        array.push(row.fields.to_csv(**options)) unless row.header_row?
-      end
 
+      if options[:encoding]
+        rows = @table.first(limit).select { |row| !row.header_row? }
+        array.push(CSV.generate_lines(rows, **options))
+      else
+        @table.first(limit).each do |row|
+          array.push(row.fields.to_csv(**options)) unless row.header_row?
+        end
+      end
       array.join("")
     end
     alias_method :to_s, :to_csv
diff --git a/test/csv/test_table.rb b/test/csv/test_table.rb
index e8ab7404..d63b32a3 100644
--- a/test/csv/test_table.rb
+++ b/test/csv/test_table.rb
@@ -373,6 +373,15 @@ def test_to_csv_limit_negative_over
     CSV
   end
 
+  def test_to_csv_encoding
+    rows  = [ CSV::Row.new(%w{A}, ["\x00\xac".force_encoding("ASCII-8BIT")]),
+              CSV::Row.new(%w{A}, ["\x00\xac"]) ]
+    table = CSV::Table.new(rows)
+
+    assert_equal('UTF-8', table.to_csv(encoding: 'UTF-8').encoding.to_s)
+    assert_raises(Encoding::CompatibilityError) {table.to_csv}
+  end
+
   def test_append
     # verify that we can chain the call
     assert_equal(@table, @table << [10, 11, 12])

From b2b6e8094f1a575c7236a2647c0112a8e5b388eb Mon Sep 17 00:00:00 2001
From: John W Higgins <wishdev@gmail.com>
Date: Wed, 2 Jul 2025 20:07:45 -0700
Subject: [PATCH 2/4] Add benchmark for Table#to_csv improvement

---
 benchmark/table.yaml | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)
 create mode 100644 benchmark/table.yaml

diff --git a/benchmark/table.yaml b/benchmark/table.yaml
new file mode 100644
index 00000000..9a67c8cd
--- /dev/null
+++ b/benchmark/table.yaml
@@ -0,0 +1,27 @@
+loop_count: 100
+contexts:
+  - gems:
+      csv: 3.3.0
+  - name: "master"
+    prelude: |
+      $LOAD_PATH.unshift(File.expand_path("lib"))
+      require "csv"
+prelude: |-
+  n_columns = Integer(ENV.fetch("N_COLUMNS", "5"), 10)
+  n_rows = Integer(ENV.fetch("N_ROWS", "100"), 10)
+  fields = ["AAAAA"] * n_columns
+  headers = n_columns.times.collect do |i|
+    "header#{i}"
+  end
+  row = CSV::Row.new(headers, fields)
+  rows = [row] * n_rows
+  table = CSV::Table.new(rows)
+  rows = [row] * n_rows * 10
+  large_table = CSV::Table.new(rows)
+benchmark:
+  "to_csv: no encoding": |-
+    table.to_csv
+  "to_csv: encoding": |-
+    table.to_csv(encoding: 'UTF-8')
+  "to_csv: encoding - 10 x rows": |-
+    large_table.to_csv(encoding: 'UTF-8')

From cf0cec0c553b8fa5568ea5c7b7c3ee4537a8e4f1 Mon Sep 17 00:00:00 2001
From: John W Higgins <wishdev@gmail.com>
Date: Fri, 4 Jul 2025 09:06:46 -0700
Subject: [PATCH 3/4] Move CSV row encoding calculation to its own method

---
 lib/csv.rb | 26 +++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/lib/csv.rb b/lib/csv.rb
index aef96ac9..ddc0b9ed 100644
--- a/lib/csv.rb
+++ b/lib/csv.rb
@@ -1506,17 +1506,7 @@ def generate_line(row, **options)
       if options[:encoding]
         str.force_encoding(options[:encoding])
       else
-        fallback_encoding = nil
-        output_encoding = nil
-        row.each do |field|
-          next unless field.is_a?(String)
-          fallback_encoding ||= field.encoding
-          next if field.ascii_only?
-          output_encoding = field.encoding
-          break
-        end
-        output_encoding ||= fallback_encoding
-        if output_encoding
+        if output_encoding = row_encoding(row)
           str.force_encoding(output_encoding)
         end
       end
@@ -1960,6 +1950,20 @@ def table(path, **options)
     private_constant :ON_WINDOWS
 
     private
+
+    def row_encoding(row)
+      fallback_encoding = nil
+      output_encoding = nil
+      row.each do |field|
+        next unless field.is_a?(String)
+        fallback_encoding ||= field.encoding
+        next if field.ascii_only?
+        output_encoding = field.encoding
+        break
+      end
+      output_encoding || fallback_encoding
+    end
+
     def may_enable_bom_detection_automatically(filename_or_io,
                                                mode,
                                                options,

From 1df04bda7e4dba65838c10a87f4f6a98bce6cc2e Mon Sep 17 00:00:00 2001
From: John W Higgins <wishdev@gmail.com>
Date: Fri, 4 Jul 2025 15:40:38 -0700
Subject: [PATCH 4/4] Update test based on @kou suggestion

---
 test/csv/test_table.rb | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/csv/test_table.rb b/test/csv/test_table.rb
index d63b32a3..7744a34b 100644
--- a/test/csv/test_table.rb
+++ b/test/csv/test_table.rb
@@ -378,7 +378,7 @@ def test_to_csv_encoding
               CSV::Row.new(%w{A}, ["\x00\xac"]) ]
     table = CSV::Table.new(rows)
 
-    assert_equal('UTF-8', table.to_csv(encoding: 'UTF-8').encoding.to_s)
+    assert_equal(Encoding::UTF_8, table.to_csv(encoding: 'UTF-8').encoding)
     assert_raises(Encoding::CompatibilityError) {table.to_csv}
   end