Force mutable Strings to address upcoming Ruby default frozen strings

examples/sample44.rb

@@ -88,7 +88,7 @@
 "rvee",
 "rveervee"
 ].each { |s|
-  p = "p_" << s
+  p = String.new("p_") << s
   g.add_nodes( p, "shape" => "point" )
   g.add_nodes( s )
   g.add_edges( p, s, "arrowhead" => s )

lib/graphviz.rb

@@ -527,7 +527,7 @@ def output( hOpts = {} )
       xOutputString = (@filename == String ||
         @output.any? {|format, file| file == String })
 
-      xOutput = ""
+      xOutput = String.new
       if @format.to_s == "none" or @output.any? {|fmt, fn| fmt.to_s == "none"}
         if xOutputString
           xOutput << xDOTScript

lib/graphviz/core_ext.rb

@@ -1,6 +1,6 @@
 class String
    def self.random(size)
-      s = ""
+      s = String.new
       d = ("a".."z").to_a + ("A".."Z").to_a + ("0".."9").to_a
       size.times {
          s << d[rand(d.size)]

lib/graphviz/dot_script.rb

@@ -51,7 +51,7 @@ class DOTScript
     def_delegators :@script, :end_with?
 
     def initialize
-      @script = ''
+      @script = String.new
     end
 
     def append(line)

lib/graphviz/edge.rb

@@ -165,10 +165,10 @@ def output( oGraphType ) #:nodoc:
       # reserved words, they aren't accepted in dot as node name
       reserved_names = ["node", "edge","graph", "digraph", "subgraph", "strict"]
 
-      xOut = reserved_names.include?(self.node_one) ? "" << "_" + self.node_one : "" << self.node_one
+      xOut = reserved_names.include?(self.node_one) ? String.new << "_" + self.node_one : String.new << self.node_one
       xOut = xOut << xLink
       xOut = reserved_names.include?(self.node_two) ? xOut << "_" + self.node_two : xOut << self.node_two
-      xAttr = ""
+      xAttr = String.new
       xSeparator = ""
       @edge_attributes.data.each do |k, v|
         xAttr << xSeparator + k + " = " + v.to_gv

lib/graphviz/node.rb

@@ -143,8 +143,8 @@ def output #:nodoc:
          # add a check to see if the node names are valid
          # if they aren't is added an _ before
          # and the print staies the same, because of the label
-         xOut = reserved_names.include?(node_id) ? "" << "_" + node_id : "" << node_id
-         xAttr = ""
+         xOut = reserved_names.include?(node_id) ? String.new << "_" + node_id : String.new << node_id
+         xAttr = String.new
          xSeparator = ""
 
          if @node_attributes.data.has_key?("label") and @node_attributes.data.has_key?("html")

lib/graphviz/xml.rb

@@ -45,7 +45,7 @@ def output( *options )
     #   * :attrs : show XML attributes (default true)
     #
     def initialize( xml_file, *options )
-      @node_name = "00000"
+      @node_name = String.new("00000")
 	   @show_text = true
 	   @show_attributes = true
 
@@ -88,7 +88,7 @@ def parse_xml_node( xml_node ) #:nodoc:
         text_node_name = local_node_name.clone
         text_node_name << "111"
 
-        xText = ""
+        xText = String.new
         xSep = ""
         xml_node.texts().each do |l|
           x = l.value.chomp.strip