diff --git a/lib/xlsxtream/core_extension.rb b/lib/xlsxtream/core_extension.rb
new file mode 100644
index 0000000..d7e839e
--- /dev/null
+++ b/lib/xlsxtream/core_extension.rb
@@ -0,0 +1,79 @@
+class Object
+  def to_xslx_value(cid, _, sst)
+    to_s.to_xslx_value(cid, false, sst)
+  end
+end
+
+class Numeric
+  def to_xslx_value(cid, _, _)
+    %Q{<c r="#{cid}" t="n"><v>#{self}</v></c>}
+  end
+end
+
+class TrueClass
+  def to_xslx_value(cid, _, _)
+    %Q{<c r="#{cid}" t="b"><v>1</v></c>}
+  end
+end
+
+class FalseClass
+  def to_xslx_value(cid, _, _)
+    %Q{<c r="#{cid}" t="b"><v>0</v></c>}
+  end
+end
+
+class Time
+  def to_xslx_value(cid, _, _)
+    # Local dates are stored as UTC by truncating the offset:
+    # 1970-01-01 00:00:00 +0200 => 1970-01-01 00:00:00 UTC
+    # This is done because SpreadsheetML is not timezone aware.
+    oa_date = (to_f + utc_offset) / 86400 + 25569
+
+    %Q{<c r="#{cid}" s="#{Xlsxtream::Row::TIME_STYLE}"><v>#{oa_date}</v></c>}
+  end
+end
+
+class DateTime
+  def to_xslx_value(cid, _, _)
+    _, jd, df, sf, of = marshal_dump
+    oa_date = jd - 2415019 + (df + of + sf / 1e9) / 86400
+
+     %Q{<c r="#{cid}" s="#{Xlsxtream::Row::TIME_STYLE}"><v>#{oa_date}</v></c>}
+  end
+end
+
+class Date
+  if RUBY_ENGINE == 'ruby'
+    def to_xslx_value(cid, _, _)
+      oa_date = (jd - 2415019).to_f
+      %Q{<c r="#{cid}" s="#{Xlsxtream::Row::DATE_STYLE}"><v>#{oa_date}</v></c>}
+    end
+  else
+    def to_xslx_value(cid, _, _)
+      oa_date = jd - 2415019 + (hour * 3600 + sec + sec_fraction.to_f) / 86400
+      %Q{<c r="#{cid}" s="#{Xlsxtream::Row::DATE_STYLE}"><v>#{oa_date}</v></c>}
+    end
+  end
+end
+
+class String
+  def to_xslx_value(cid, auto_format, sst)
+    if empty?
+      ""
+    elsif auto_format
+      Xlsxtream::Row.auto_format(self).to_xslx_value(cid, false, sst)
+    else
+      if encoding != Xlsxtream::Row::ENCODING
+        value = encode(Xlsxtream::Row::ENCODING)
+      else
+        value = self
+      end
+
+      if sst
+        %Q{<c r="#{cid}" t="s"><v>#{sst[value]}</v></c>}
+      else
+        %Q{<c r="#{cid}" t="inlineStr"><is><t>#{Xlsxtream::XML.escape_value(value)}</t></is></c>}
+      end
+    end
+  end
+end
diff --git a/lib/xlsxtream/row.rb b/lib/xlsxtream/row.rb
index afba661..a7720a9 100644
--- a/lib/xlsxtream/row.rb
+++ b/lib/xlsxtream/row.rb
@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 require "date"
+require "xlsxtream/core_extension"
 require "xlsxtream/xml"
 
 module Xlsxtream
@@ -31,85 +32,33 @@ def to_xml
       xml = String.new(%Q{<row r="#{@rownum}">})
 
       @row.each do |value|
-        cid = "#{column}#{@rownum}"
-        column.next!
-
-        if @auto_format && value.is_a?(String)
-          value = auto_format(value)
-        end
-
-        case value
-        when Numeric
-          xml << %Q{<c r="#{cid}" t="n"><v>#{value}</v></c>}
-        when TrueClass, FalseClass
-          xml << %Q{<c r="#{cid}" t="b"><v>#{value ? 1 : 0}</v></c>}
-        when Time
-          xml << %Q{<c r="#{cid}" s="#{TIME_STYLE}"><v>#{time_to_oa_date(value)}</v></c>}
-        when DateTime
-          xml << %Q{<c r="#{cid}" s="#{TIME_STYLE}"><v>#{datetime_to_oa_date(value)}</v></c>}
-        when Date
-          xml << %Q{<c r="#{cid}" s="#{DATE_STYLE}"><v>#{date_to_oa_date(value)}</v></c>}
-        else
-          value = value.to_s
-
-          unless value.empty? # no xml output for for empty strings
-            value = value.encode(ENCODING) if value.encoding != ENCODING
-
-            if @sst
-              xml << %Q{<c r="#{cid}" t="s"><v>#{@sst[value]}</v></c>}
-            else
-              xml << %Q{<c r="#{cid}" t="inlineStr"><is><t>#{XML.escape_value(value)}</t></is></c>}
-            end
-          end
+        unless value.nil?
+          xml << value.to_xslx_value("#{column}#{@rownum}", @auto_format, @sst)
         end
+        column.next!
       end
 
       xml << '</row>'
     end
 
-    private
-
     # Detects and casts numbers, date, time in text
-    def auto_format(value)
-      case value
-      when TRUE_STRING
-        true
-      when FALSE_STRING
-        false
-      when NUMBER_PATTERN
-        value.include?('.') ? value.to_f : value.to_i
-      when DATE_PATTERN
-        Date.parse(value) rescue value
-      when TIME_PATTERN
-        DateTime.parse(value) rescue value
-      else
-        value
-      end
-    end
-
-    # Converts Time instance to OLE Automation Date
-    def time_to_oa_date(time)
-      # Local dates are stored as UTC by truncating the offset:
-      # 1970-01-01 00:00:00 +0200 => 1970-01-01 00:00:00 UTC
-      # This is done because SpreadsheetML is not timezone aware.
-      (time.to_f + time.utc_offset) / 86400 + 25569
-    end
-
-    # Converts DateTime instance to OLE Automation Date
-    if RUBY_ENGINE == 'ruby'
-      def datetime_to_oa_date(date)
-        _, jd, df, sf, of = date.marshal_dump
-        jd - 2415019 + (df + of + sf / 1e9) / 86400
-      end
-    else
-      def datetime_to_oa_date(date)
-        date.jd - 2415019 + (date.hour * 3600 + date.sec + date.sec_fraction.to_f) / 86400
+    class << self
+      def auto_format(value)
+        case value
+        when TRUE_STRING
+          true
+        when FALSE_STRING
+          false
+        when NUMBER_PATTERN
+          value.include?('.') ? value.to_f : value.to_i
+        when DATE_PATTERN
+          Date.parse(value) rescue value
+        when TIME_PATTERN
+          DateTime.parse(value) rescue value
+        else
+          value
+        end
       end
     end
-
-    # Converts Date instance to OLE Automation Date
-    def date_to_oa_date(date)
-      (date.jd - 2415019).to_f
-    end
   end
 end