Import CSV 3.0.2

This includes performance improvement especially writing. Writing is
about 2 times faster.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66507 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

7 files changed, 997 insertions, 9 deletions

diff --git a/lib/csv/csv.gemspec b/lib/csv/csv.gemspec
index fae5caae19..0c9d265584 100644
--- a/lib/csv/csv.gemspec
+++ b/lib/csv/csv.gemspec
@@ -18,12 +18,26 @@ Gem::Specification.new do |spec|
   spec.homepage      = "https://github.com/ruby/csv"
   spec.license       = "BSD-2-Clause"
 
-  spec.files         = ["lib/csv.rb", "lib/csv/table.rb", "lib/csv/core_ext/string.rb", "lib/csv/core_ext/array.rb", "lib/csv/row.rb", "lib/csv/version.rb"]
-  spec.files         += ["README.md", "LICENSE.txt", "news.md"]
+  spec.files         = [
+    "LICENSE.txt",
+    "NEWS.md",
+    "README.md",
+    "lib/csv.rb",
+    "lib/csv/core_ext/array.rb",
+    "lib/csv/core_ext/string.rb",
+    "lib/csv/fields_converter.rb",
+    "lib/csv/match_p.rb",
+    "lib/csv/parser.rb",
+    "lib/csv/row.rb",
+    "lib/csv/table.rb",
+    "lib/csv/version.rb",
+    "lib/csv/writer.rb",
+  ]
   spec.require_paths = ["lib"]
   spec.required_ruby_version = ">= 2.3.0"
 
   spec.add_development_dependency "bundler"
   spec.add_development_dependency "rake"
   spec.add_development_dependency "benchmark-ips"
+  spec.add_development_dependency "simplecov"
 end
diff --git a/lib/csv/fields_converter.rb b/lib/csv/fields_converter.rb
new file mode 100644
index 0000000000..c2fa5798ff
--- /dev/null
+++ b/lib/csv/fields_converter.rb
@@ -0,0 +1,78 @@
+# frozen_string_literal: true
+
+class CSV
+  class FieldsConverter
+    include Enumerable
+
+    def initialize(options={})
+      @converters = []
+      @nil_value = options[:nil_value]
+      @empty_value = options[:empty_value]
+      @empty_value_is_empty_string = (@empty_value == "")
+      @accept_nil = options[:accept_nil]
+      @builtin_converters = options[:builtin_converters]
+      @need_static_convert = need_static_convert?
+    end
+
+    def add_converter(name=nil, &converter)
+      if name.nil?  # custom converter
+        @converters << converter
+      else          # named converter
+        combo = @builtin_converters[name]
+        case combo
+        when Array  # combo converter
+          combo.each do |sub_name|
+            add_converter(sub_name)
+          end
+        else        # individual named converter
+          @converters << combo
+        end
+      end
+    end
+
+    def each(&block)
+      @converters.each(&block)
+    end
+
+    def empty?
+      @converters.empty?
+    end
+
+    def convert(fields, headers, lineno)
+      return fields unless need_convert?
+
+      fields.collect.with_index do |field, index|
+        if field.nil?
+          field = @nil_value
+        elsif field.empty?
+          field = @empty_value unless @empty_value_is_empty_string
+        end
+        @converters.each do |converter|
+          break if field.nil? and @accept_nil
+          if converter.arity == 1  # straight field converter
+            field = converter[field]
+          else                     # FieldInfo converter
+            if headers
+              header = headers[index]
+            else
+              header = nil
+            end
+            field = converter[field, FieldInfo.new(index, lineno, header)]
+          end
+          break unless field.is_a?(String)  # short-circuit pipeline for speed
+        end
+        field  # final state of each field, converted or original
+      end
+    end
+
+    private
+    def need_static_convert?
+      not (@nil_value.nil? and @empty_value_is_empty_string)
+    end
+
+    def need_convert?
+      @need_static_convert or
+        (not @converters.empty?)
+    end
+  end
+end
diff --git a/lib/csv/match_p.rb b/lib/csv/match_p.rb
new file mode 100644
index 0000000000..775559a3eb
--- /dev/null
+++ b/lib/csv/match_p.rb
@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+# This provides String#match? and Regexp#match? for Ruby 2.3.
+unless String.method_defined?(:match?)
+  class CSV
+    module MatchP
+      refine String do
+        def match?(pattern)
+          self =~ pattern
+        end
+      end
+
+      refine Regexp do
+        def match?(string)
+          self =~ string
+        end
+      end
+    end
+  end
+end
diff --git a/lib/csv/parser.rb b/lib/csv/parser.rb
new file mode 100644
index 0000000000..2682c27ea3
--- /dev/null
+++ b/lib/csv/parser.rb
@@ -0,0 +1,713 @@
+# frozen_string_literal: true
+
+require "strscan"
+
+require_relative "match_p"
+require_relative "row"
+require_relative "table"
+
+using CSV::MatchP if CSV.const_defined?(:MatchP)
+
+class CSV
+  class Parser
+    class InvalidEncoding < StandardError
+    end
+
+    class Scanner < StringScanner
+      alias_method :scan_all, :scan
+
+      def initialize(*args)
+        super
+        @keeps = []
+      end
+
+      def keep_start
+        @keeps.push(pos)
+      end
+
+      def keep_end
+        start = @keeps.pop
+        string[start, pos - start]
+      end
+
+      def keep_back
+        self.pos = @keeps.pop
+      end
+
+      def keep_drop
+        @keeps.pop
+      end
+    end
+
+    class InputsScanner
+      def initialize(inputs, encoding, chunk_size: 8192)
+        @inputs = inputs.dup
+        @encoding = encoding
+        @chunk_size = chunk_size
+        @last_scanner = @inputs.empty?
+        @keeps = []
+        read_chunk
+      end
+
+      def scan(pattern)
+        value = @scanner.scan(pattern)
+        return value if @last_scanner
+
+        if value
+          read_chunk if @scanner.eos?
+          return value
+        else
+          nil
+        end
+      end
+
+      def scan_all(pattern)
+        value = @scanner.scan(pattern)
+        return value if @last_scanner
+
+        return nil if value.nil?
+        while @scanner.eos? and read_chunk and (sub_value = @scanner.scan(pattern))
+          value << sub_value
+        end
+        value
+      end
+
+      def eos?
+        @scanner.eos?
+      end
+
+      def keep_start
+        @keeps.push([@scanner.pos, nil])
+      end
+
+      def keep_end
+        start, buffer = @keeps.pop
+        keep = @scanner.string[start, @scanner.pos - start]
+        if buffer
+          buffer << keep
+          keep = buffer
+        end
+        keep
+      end
+
+      def keep_back
+        start, buffer = @keeps.pop
+        if buffer
+          string = @scanner.string
+          keep = string[start, string.size - start]
+          if keep and not keep.empty?
+            @inputs.unshift(StringIO.new(keep))
+            @last_scanner = false
+          end
+          @scanner = StringScanner.new(buffer)
+        else
+          @scanner.pos = start
+        end
+      end
+
+      def keep_drop
+        @keeps.pop
+      end
+
+      def rest
+        @scanner.rest
+      end
+
+      private
+      def read_chunk
+        return false if @last_scanner
+
+        unless @keeps.empty?
+          keep = @keeps.last
+          keep_start = keep[0]
+          string = @scanner.string
+          keep_data = string[keep_start, @scanner.pos - keep_start]
+          if keep_data
+            keep_buffer = keep[1]
+            if keep_buffer
+              keep_buffer << keep_data
+            else
+              keep[1] = keep_data.dup
+            end
+          end
+          keep[0] = 0
+        end
+
+        input = @inputs.first
+        case input
+        when StringIO
+          string = input.string
+          raise InvalidEncoding unless string.valid_encoding?
+          @scanner = StringScanner.new(string)
+          @inputs.shift
+          @last_scanner = @inputs.empty?
+          true
+        else
+          chunk = input.gets(nil, @chunk_size)
+          if chunk
+            raise InvalidEncoding unless chunk.valid_encoding?
+            @scanner = StringScanner.new(chunk)
+            if input.respond_to?(:eof?) and input.eof?
+              @inputs.shift
+              @last_scanner = @inputs.empty?
+            end
+            true
+          else
+            @scanner = StringScanner.new("".encode(@encoding))
+            @inputs.shift
+            @last_scanner = @inputs.empty?
+            if @last_scanner
+              false
+            else
+              read_chunk
+            end
+          end
+        end
+      end
+    end
+
+    def initialize(input, options)
+      @input = input
+      @options = options
+      @samples = []
+
+      prepare
+    end
+
+    def column_separator
+      @column_separator
+    end
+
+    def row_separator
+      @row_separator
+    end
+
+    def quote_character
+      @quote_character
+    end
+
+    def field_size_limit
+      @field_size_limit
+    end
+
+    def skip_lines
+      @skip_lines
+    end
+
+    def unconverted_fields?
+      @unconverted_fields
+    end
+
+    def headers
+      @headers
+    end
+
+    def header_row?
+      @use_headers and @headers.nil?
+    end
+
+    def return_headers?
+      @return_headers
+    end
+
+    def skip_blanks?
+      @skip_blanks
+    end
+
+    def liberal_parsing?
+      @liberal_parsing
+    end
+
+    def lineno
+      @lineno
+    end
+
+    def line
+      last_line
+    end
+
+    def parse(&block)
+      return to_enum(__method__) unless block_given?
+
+      if @return_headers and @headers
+        headers = Row.new(@headers, @raw_headers, true)
+        if @unconverted_fields
+          headers = add_unconverted_fields(headers, [])
+        end
+        yield headers
+      end
+
+      row = []
+      begin
+        @scanner = build_scanner
+        skip_needless_lines
+        start_row
+        while true
+          @quoted_column_value = false
+          @unquoted_column_value = false
+          value = parse_column_value
+          if value and @field_size_limit and value.size >= @field_size_limit
+            raise MalformedCSVError.new("Field size exceeded", @lineno + 1)
+          end
+          if parse_column_end
+            row << value
+          elsif parse_row_end
+            if row.empty? and value.nil?
+              emit_row([], &block) unless @skip_blanks
+            else
+              row << value
+              emit_row(row, &block)
+              row = []
+            end
+            skip_needless_lines
+            start_row
+          elsif @scanner.eos?
+            return if row.empty? and value.nil?
+            row << value
+            emit_row(row, &block)
+            return
+          else
+            if @quoted_column_value
+              message = "Do not allow except col_sep_split_separator " +
+                "after quoted fields"
+              raise MalformedCSVError.new(message, @lineno + 1)
+            elsif @unquoted_column_value and @scanner.scan(@cr_or_lf)
+              message = "Unquoted fields do not allow \\r or \\n"
+              raise MalformedCSVError.new(message, @lineno + 1)
+            elsif @scanner.rest.start_with?(@quote_character)
+              message = "Illegal quoting"
+              raise MalformedCSVError.new(message, @lineno + 1)
+            else
+              raise MalformedCSVError.new("TODO: Meaningful message",
+                                          @lineno + 1)
+            end
+          end
+        end
+      rescue InvalidEncoding
+        message = "Invalid byte sequence in #{@encoding}"
+        raise MalformedCSVError.new(message, @lineno + 1)
+      end
+    end
+
+    private
+    def prepare
+      prepare_variable
+      prepare_regexp
+      prepare_line
+      prepare_header
+      prepare_parser
+    end
+
+    def prepare_variable
+      @encoding = @options[:encoding]
+      @liberal_parsing = @options[:liberal_parsing]
+      @unconverted_fields = @options[:unconverted_fields]
+      @field_size_limit = @options[:field_size_limit]
+      @skip_blanks = @options[:skip_blanks]
+      @fields_converter = @options[:fields_converter]
+      @header_fields_converter = @options[:header_fields_converter]
+    end
+
+    def prepare_regexp
+      @column_separator = @options[:column_separator].to_s.encode(@encoding)
+      @row_separator =
+        resolve_row_separator(@options[:row_separator]).encode(@encoding)
+      @quote_character = @options[:quote_character].to_s.encode(@encoding)
+      if @quote_character.length != 1
+        raise ArgumentError, ":quote_char has to be a single character String"
+      end
+
+      escaped_column_separator = Regexp.escape(@column_separator)
+      escaped_row_separator = Regexp.escape(@row_separator)
+      escaped_quote_character = Regexp.escape(@quote_character)
+
+      skip_lines = @options[:skip_lines]
+      case skip_lines
+      when String
+        @skip_lines = skip_lines.encode(@encoding)
+      when Regexp, nil
+        @skip_lines = skip_lines
+      else
+        unless skip_lines.respond_to?(:match)
+          message =
+            ":skip_lines has to respond to \#match: #{skip_lines.inspect}"
+          raise ArgumentError, message
+        end
+        @skip_lines = skip_lines
+      end
+
+      @column_end = Regexp.new(escaped_column_separator)
+      if @column_separator.size > 1
+        @column_ends = @column_separator.each_char.collect do |char|
+          Regexp.new(Regexp.escape(char))
+        end
+      else
+        @column_ends = nil
+      end
+      @row_end = Regexp.new(escaped_row_separator)
+      if @row_separator.size > 1
+        @row_ends = @row_separator.each_char.collect do |char|
+          Regexp.new(Regexp.escape(char))
+        end
+      else
+        @row_ends = nil
+      end
+      @quotes = Regexp.new(escaped_quote_character +
+                           "+".encode(@encoding))
+      @quoted_value = Regexp.new("[^".encode(@encoding) +
+                                 escaped_quote_character +
+                                 "]+".encode(@encoding))
+      if @liberal_parsing
+        @unquoted_value = Regexp.new("[^".encode(@encoding) +
+                                     escaped_column_separator +
+                                     "\r\n]+".encode(@encoding))
+      else
+        @unquoted_value = Regexp.new("[^".encode(@encoding) +
+                                     escaped_quote_character +
+                                     escaped_column_separator +
+                                     "\r\n]+".encode(@encoding))
+      end
+      @cr_or_lf = Regexp.new("[\r\n]".encode(@encoding))
+      @not_line_end = Regexp.new("[^\r\n]+".encode(@encoding))
+    end
+
+    def resolve_row_separator(separator)
+      if separator == :auto
+        cr = "\r".encode(@encoding)
+        lf = "\n".encode(@encoding)
+        if @input.is_a?(StringIO)
+          separator = detect_row_separator(@input.string, cr, lf)
+        elsif @input.respond_to?(:gets)
+          if @input.is_a?(File)
+            chunk_size = 32 * 1024
+          else
+            chunk_size = 1024
+          end
+          begin
+            while separator == :auto
+              #
+              # if we run out of data, it's probably a single line
+              # (ensure will set default value)
+              #
+              break unless sample = @input.gets(nil, chunk_size)
+
+              # extend sample if we're unsure of the line ending
+              if sample.end_with?(cr)
+                sample << (@input.gets(nil, 1) || "")
+              end
+
+              @samples << sample
+
+              separator = detect_row_separator(sample, cr, lf)
+            end
+          rescue IOError
+            # do nothing:  ensure will set default
+          end
+        end
+        separator = $INPUT_RECORD_SEPARATOR if separator == :auto
+      end
+      separator.to_s.encode(@encoding)
+    end
+
+    def detect_row_separator(sample, cr, lf)
+      lf_index = sample.index(lf)
+      if lf_index
+        cr_index = sample[0, lf_index].index(cr)
+      else
+        cr_index = sample.index(cr)
+      end
+      if cr_index and lf_index
+        if cr_index + 1 == lf_index
+          cr + lf
+        elsif cr_index < lf_index
+          cr
+        else
+          lf
+        end
+      elsif cr_index
+        cr
+      elsif lf_index
+        lf
+      else
+        :auto
+      end
+    end
+
+    def prepare_line
+      @lineno = 0
+      @last_line = nil
+      @scanner = nil
+    end
+
+    def last_line
+      if @scanner
+        @last_line ||= @scanner.keep_end
+      else
+        @last_line
+      end
+    end
+
+    def prepare_header
+      @return_headers = @options[:return_headers]
+
+      headers = @options[:headers]
+      case headers
+      when Array
+        @raw_headers = headers
+        @use_headers = true
+      when String
+        @raw_headers = parse_headers(headers)
+        @use_headers = true
+      when nil, false
+        @raw_headers = nil
+        @use_headers = false
+      else
+        @raw_headers = nil
+        @use_headers = true
+      end
+      if @raw_headers
+        @headers = adjust_headers(@raw_headers)
+      else
+        @headers = nil
+      end
+    end
+
+    def parse_headers(row)
+      CSV.parse_line(row,
+                     col_sep:    @column_separator,
+                     row_sep:    @row_separator,
+                     quote_char: @quote_character)
+    end
+
+    def adjust_headers(headers)
+      adjusted_headers = @header_fields_converter.convert(headers, nil, @lineno)
+      adjusted_headers.each {|h| h.freeze if h.is_a? String}
+      adjusted_headers
+    end
+
+    def prepare_parser
+      @may_quoted = may_quoted?
+    end
+
+    def may_quoted?
+      if @input.is_a?(StringIO)
+        sample = @input.string
+      else
+        return false if @samples.empty?
+        sample = @samples.first
+      end
+      sample[0, 128].index(@quote_character)
+    end
+
+    SCANNER_TEST = (ENV["CSV_PARSER_SCANNER_TEST"] == "yes")
+    if SCANNER_TEST
+      class UnoptimizedStringIO
+        def initialize(string)
+          @io = StringIO.new(string)
+        end
+
+        def gets(*args)
+          @io.gets(*args)
+        end
+
+        def eof?
+          @io.eof?
+        end
+      end
+
+      def build_scanner
+        inputs = @samples.collect do |sample|
+          UnoptimizedStringIO.new(sample)
+        end
+        if @input.is_a?(StringIO)
+          inputs << UnoptimizedStringIO.new(@input.string)
+        else
+          inputs << @input
+        end
+        InputsScanner.new(inputs, @encoding, chunk_size: 1)
+      end
+    else
+      def build_scanner
+        string = nil
+        if @samples.empty? and @input.is_a?(StringIO)
+          string = @input.string
+        elsif @samples.size == 1 and @input.respond_to?(:eof?) and @input.eof?
+          string = @samples[0]
+        end
+        if string
+          unless string.valid_encoding?
+            message = "Invalid byte sequence in #{@encoding}"
+            raise MalformedCSVError.new(message, @lineno + 1)
+          end
+          Scanner.new(string)
+        else
+          inputs = @samples.collect do |sample|
+            StringIO.new(sample)
+          end
+          inputs << @input
+          InputsScanner.new(inputs, @encoding)
+        end
+      end
+    end
+
+    def skip_needless_lines
+      return unless @skip_lines
+
+      while true
+        @scanner.keep_start
+        line = @scanner.scan_all(@not_line_end) || "".encode(@encoding)
+        line << @row_separator if parse_row_end
+        if skip_line?(line)
+          @scanner.keep_drop
+        else
+          @scanner.keep_back
+          return
+        end
+      end
+    end
+
+    def skip_line?(line)
+      case @skip_lines
+      when String
+        line.include?(@skip_lines)
+      when Regexp
+        @skip_lines.match?(line)
+      else
+        @skip_lines.match(line)
+      end
+    end
+
+    def parse_column_value
+      if @liberal_parsing
+        quoted_value = parse_quoted_column_value
+        if quoted_value
+          unquoted_value = parse_unquoted_column_value
+          if unquoted_value
+            @quote_character + quoted_value + @quote_character + unquoted_value
+          else
+            quoted_value
+          end
+        else
+          parse_unquoted_column_value
+        end
+      elsif @may_quoted
+        parse_quoted_column_value ||
+          parse_unquoted_column_value
+      else
+        parse_unquoted_column_value ||
+          parse_quoted_column_value
+      end
+    end
+
+    def parse_unquoted_column_value
+      value = @scanner.scan_all(@unquoted_value)
+      @unquoted_column_value = true if value
+      value
+    end
+
+    def parse_quoted_column_value
+      quotes = @scanner.scan_all(@quotes)
+      return nil unless quotes
+
+      @quoted_column_value = true
+      n_quotes = quotes.size
+      if (n_quotes % 2).zero?
+        quotes[0, (n_quotes - 2) / 2]
+      else
+        value = quotes[0, (n_quotes - 1) / 2]
+        while true
+          quoted_value = @scanner.scan_all(@quoted_value)
+          value << quoted_value if quoted_value
+          quotes = @scanner.scan_all(@quotes)
+          unless quotes
+            message = "Unclosed quoted field"
+            raise MalformedCSVError.new(message, @lineno + 1)
+          end
+          n_quotes = quotes.size
+          if n_quotes == 1
+            break
+          elsif (n_quotes % 2) == 1
+            value << quotes[0, (n_quotes - 1) / 2]
+            break
+          else
+            value << quotes[0, n_quotes / 2]
+          end
+        end
+        value
+      end
+    end
+
+    def parse_column_end
+      return true if @scanner.scan(@column_end)
+      return false unless @column_ends
+
+      @scanner.keep_start
+      if @column_ends.all? {|column_end| @scanner.scan(column_end)}
+        @scanner.keep_drop
+        true
+      else
+        @scanner.keep_back
+        false
+      end
+    end
+
+    def parse_row_end
+      return true if @scanner.scan(@row_end)
+      return false unless @row_ends
+      @scanner.keep_start
+      if @row_ends.all? {|row_end| @scanner.scan(row_end)}
+        @scanner.keep_drop
+        true
+      else
+        @scanner.keep_back
+        false
+      end
+    end
+
+    def start_row
+      if @last_line
+        @last_line = nil
+      else
+        @scanner.keep_drop
+      end
+      @scanner.keep_start
+    end
+
+    def emit_row(row, &block)
+      @lineno += 1
+
+      raw_row = row
+      if @use_headers
+        if @headers.nil?
+          @headers = adjust_headers(row)
+          return unless @return_headers
+          row = Row.new(@headers, row, true)
+        else
+          row = Row.new(@headers,
+                        @fields_converter.convert(raw_row, @headers, @lineno))
+        end
+      else
+        # convert fields, if needed...
+        row = @fields_converter.convert(raw_row, nil, @lineno)
+      end
+
+      # inject unconverted fields and accessor, if requested...
+      if @unconverted_fields and not row.respond_to?(:unconverted_fields)
+        add_unconverted_fields(row, raw_row)
+      end
+
+      yield(row)
+    end
+
+    # This method injects an instance variable <tt>unconverted_fields</tt> into
+    # +row+ and an accessor method for +row+ called unconverted_fields().  The
+    # variable is set to the contents of +fields+.
+    def add_unconverted_fields(row, fields)
+      class << row
+        attr_reader :unconverted_fields
+      end
+      row.instance_variable_set(:@unconverted_fields, fields)
+      row
+    end
+  end
+end
diff --git a/lib/csv/table.rb b/lib/csv/table.rb
index 17a7c542e4..b13d1ada10 100644
--- a/lib/csv/table.rb
+++ b/lib/csv/table.rb
@@ -16,6 +16,11 @@ class CSV
     # Construct a new CSV::Table from +array_of_rows+, which are expected
     # to be CSV::Row objects.  All rows are assumed to have the same headers.
     #
+    # The optional +headers+ parameter can be set to Array of headers.
+    # If headers aren't set, headers are fetched from CSV::Row objects.
+    # Otherwise, headers() method will return headers being set in
+    # headers arugument.
+    #
     # A CSV::Table object supports the following Array methods through
     # delegation:
     #
@@ -23,8 +28,17 @@ class CSV
     # * length()
     # * size()
     #
-    def initialize(array_of_rows)
+    def initialize(array_of_rows, headers: nil)
       @table = array_of_rows
+      @headers = headers
+      unless @headers
+        if @table.empty?
+          @headers = []
+        else
+          @headers = @table.first.headers
+        end
+      end
+
       @mode  = :col_or_row
     end
 
@@ -122,11 +136,7 @@ class CSV
     # other rows).  An empty Array is returned for empty tables.
     #
     def headers
-      if @table.empty?
-        Array.new
-      else
-        @table.first.headers
-      end
+      @headers.dup
     end
 
     #
@@ -171,6 +181,10 @@ class CSV
           @table[index_or_header] = value
         end
       else                 # set column
+        unless index_or_header.is_a? Integer
+          index = @headers.index(index_or_header) || @headers.size
+          @headers[index] = index_or_header
+        end
         if value.is_a? Array  # multiple values
           @table.each_with_index do |row, i|
             if row.header_row?
@@ -258,6 +272,11 @@ class CSV
             (@mode == :col_or_row and index_or_header.is_a? Integer)
           @table.delete_at(index_or_header)
         else                 # by header
+          if index_or_header.is_a? Integer
+            @headers.delete_at(index_or_header)
+          else
+            @headers.delete(index_or_header)
+          end
           @table.map { |row| row.delete(index_or_header).last }
         end
       end
diff --git a/lib/csv/version.rb b/lib/csv/version.rb
index d62a093418..d6b59b3097 100644
--- a/lib/csv/version.rb
+++ b/lib/csv/version.rb
@@ -2,5 +2,5 @@
 
 class CSV
   # The version of the installed library.
-  VERSION = "3.0.1"
+  VERSION = "3.0.2"
 end
diff --git a/lib/csv/writer.rb b/lib/csv/writer.rb
new file mode 100644
index 0000000000..2f2ab095d7
--- /dev/null
+++ b/lib/csv/writer.rb
@@ -0,0 +1,144 @@
+# frozen_string_literal: true
+
+require_relative "match_p"
+require_relative "row"
+
+using CSV::MatchP if CSV.const_defined?(:MatchP)
+
+class CSV
+  class Writer
+    attr_reader :lineno
+    attr_reader :headers
+
+    def initialize(output, options)
+      @output = output
+      @options = options
+      @lineno = 0
+      prepare
+      if @options[:write_headers] and @headers
+        self << @headers
+      end
+    end
+
+    def <<(row)
+      case row
+      when Row
+        row = row.fields
+      when Hash
+        row = @headers.collect {|header| row[header]}
+      end
+
+      @headers ||= row if @use_headers
+      @lineno += 1
+
+      line = row.collect(&@quote).join(@column_separator) + @row_separator
+      if @output_encoding
+        line = line.encode(@output_encoding)
+      end
+      @output << line
+
+      self
+    end
+
+    def rewind
+      @lineno = 0
+      @headers = nil if @options[:headers].nil?
+    end
+
+    private
+    def prepare
+      @encoding = @options[:encoding]
+
+      prepare_header
+      prepare_format
+      prepare_output
+    end
+
+    def prepare_header
+      headers = @options[:headers]
+      case headers
+      when Array
+        @headers = headers
+        @use_headers = true
+      when String
+        @headers = CSV.parse_line(headers,
+                                  col_sep: @options[:column_separator],
+                                  row_sep: @options[:row_separator],
+                                  quote_char: @options[:quote_character])
+        @use_headers = true
+      when true
+        @headers = nil
+        @use_headers = true
+      else
+        @headers = nil
+        @use_headers = false
+      end
+      return unless @headers
+
+      converter = @options[:header_fields_converter]
+      @headers = converter.convert(@headers, nil, 0)
+      @headers.each do |header|
+        header.freeze if header.is_a?(String)
+      end
+    end
+
+    def prepare_format
+      @column_separator = @options[:column_separator].to_s.encode(@encoding)
+      row_separator = @options[:row_separator]
+      if row_separator == :auto
+        @row_separator = $INPUT_RECORD_SEPARATOR.encode(@encoding)
+      else
+        @row_separator = row_separator.to_s.encode(@encoding)
+      end
+      quote_character = @options[:quote_character]
+      quote = lambda do |field|
+        field = String(field)
+        encoded_quote_character = quote_character.encode(field.encoding)
+        encoded_quote_character +
+          field.gsub(encoded_quote_character,
+                     encoded_quote_character * 2) +
+          encoded_quote_character
+      end
+      if @options[:force_quotes]
+        @quote = quote
+      else
+        quotable_pattern =
+          Regexp.new("[\r\n".encode(@encoding) +
+                     Regexp.escape(@column_separator) +
+                     Regexp.escape(quote_character.encode(@encoding)) +
+                     "]".encode(@encoding))
+        @quote = lambda do |field|
+          if field.nil?  # represent +nil+ fields as empty unquoted fields
+            ""
+          else
+            field = String(field)  # Stringify fields
+            # represent empty fields as empty quoted fields
+            if field.empty? or quotable_pattern.match?(field)
+              quote.call(field)
+            else
+              field  # unquoted field
+            end
+          end
+        end
+      end
+    end
+
+    def prepare_output
+      @output_encoding = nil
+      return unless @output.is_a?(StringIO)
+
+      output_encoding = @output.internal_encoding || @output.external_encoding
+      if @encoding != output_encoding
+        if @options[:force_encoding]
+          @output_encoding = output_encoding
+        else
+          compatible_encoding = Encoding.compatible?(@encoding, output_encoding)
+          if compatible_encoding
+            @output.set_encoding(compatible_encoding)
+            @output.seek(0, IO::SEEK_END)
+          end
+        end
+      end
+    end
+  end
+end