Only open struct class if there is actually already a class

mrblib/struct.rb

@@ -2,45 +2,49 @@
 # Struct
 #
 # ISO 15.2.18
-class Struct
 
-  ##
-  # Calls the given block for each element of +self+
-  # and pass the respective element.
-  #
-  # ISO 15.2.18.4.4
-  def each(&block)
-    self.class.members.each{|field|
-      block.call(self[field])
-    }
-    self
-  end
+if Object.const_defined?(:Struct)
+  class Struct
 
-  ##
-  # Calls the given block for each element of +self+
-  # and pass the name and value of the respectiev
-  # element.
-  #
-  # ISO 15.2.18.4.5
-  def each_pair(&block)
-    self.class.members.each{|field|
-      block.call(field.to_sym, self[field])
-    }
-    self
-  end
+    ##
+    # Calls the given block for each element of +self+
+    # and pass the respective element.
+    #
+    # ISO 15.2.18.4.4
+    def each(&block)
+      self.class.members.each{|field|
+        block.call(self[field])
+      }
+      self
+    end
 
-  ##
-  # Calls the given block for each element of +self+
-  # and returns an array with all elements of which
-  # block is not false.
-  #
-  # ISO 15.2.18.4.7
-  def select(&block)
-    ary = []
-    self.class.members.each{|field|
-      val = self[field]
-      ary.push(val) if block.call(val)
-    }
-    ary
+    ##
+    # Calls the given block for each element of +self+
+    # and pass the name and value of the respectiev
+    # element.
+    #
+    # ISO 15.2.18.4.5
+    def each_pair(&block)
+      self.class.members.each{|field|
+        block.call(field.to_sym, self[field])
+      }
+      self
+    end
+
+    ##
+    # Calls the given block for each element of +self+
+    # and returns an array with all elements of which
+    # block is not false.
+    #
+    # ISO 15.2.18.4.7
+    def select(&block)
+      ary = []
+      self.class.members.each{|field|
+        val = self[field]
+        ary.push(val) if block.call(val)
+      }
+      ary
+    end
   end
 end
+