[ruby/ostruct] Allow overriding public methods

[Fixes https://bugs.ruby-lang.org/issues/15409]

lib/ostruct.rb

@@ -100,9 +100,9 @@ class OpenStruct
 
   # Duplicates an OpenStruct object's Hash table.
   def initialize_copy(orig) # :nodoc:
+    orig.table.each_key{|key| new_ostruct_member!(key)}
     super
     @table = @table.dup
-    @table.each_key{|key| new_ostruct_member!(key)}
   end
 
   #
@@ -159,8 +159,8 @@ class OpenStruct
   # Provides marshalling support for use by the Marshal library.
   #
   def marshal_load(x)
+    x.each_key{|key| new_ostruct_member!(key)}
     @table = x
-    @table.each_key{|key| new_ostruct_member!(key)}
   end
 
   #
@@ -169,7 +169,7 @@ class OpenStruct
   # define_singleton_method for both the getter method and the setter method.
   #
   def new_ostruct_member!(name) # :nodoc:
-    unless respond_to?(name)
+    unless @table.key?(name)
       define_singleton_method(name) { @table[name] }
       define_singleton_method("#{name}=") {|x| @table[name] = x}
     end

test/ostruct/test_ostruct.rb

@@ -235,4 +235,10 @@ class TC_OpenStruct < Test::Unit::TestCase
     assert_equal(:foo, os.puts)
     assert_equal(:bar, os.format)
   end
+
+  def test_overriden_public_methods
+    os = OpenStruct.new(method: :foo, class: :bar)
+    assert_equal(:foo, os.method)
+    assert_equal(:bar, os.class)
+  end
 end