Fallback value to OpenStruct delete_field

lib/ostruct.rb

@@ -285,7 +285,9 @@ def dig(name, *names)
 
   #
   # Removes the named field from the object. Returns the value that the field
-  # contained if it was defined.
+  # contained if it was defined, else a NameError is raised.
+  # Optionally, provide a value that will be returned in the event the
+  # deleting field does not exist.
   #
   #   require "ostruct"
   #
@@ -299,13 +301,18 @@ def dig(name, *names)
   #   person.pension = nil
   #   person                 # => #<OpenStruct name="John", pension=nil>
   #
+  #   person.delete_field('number')  # => NameError
+  #
+  #   person.delete_field('number') { 8675_309 } # => 8675309
+  #
   def delete_field(name)
     sym = name.to_sym
     begin
       singleton_class.remove_method(sym, "#{sym}=")
     rescue NameError
     end
     @table.delete(sym) do
+      return yield if block_given?
       raise NameError.new("no field `#{sym}' in #{self}", sym)
     end
   end

test/ostruct/test_ostruct.rb

@@ -89,7 +89,7 @@ def test_delete_field
     a = o.delete_field :a
     assert_not_respond_to(o, :a, bug)
     assert_not_respond_to(o, :a=, bug)
-    assert_equal(a, 'a')
+    assert_equal('a', a)
     s = Object.new
     def s.to_sym
       :foo
@@ -100,6 +100,16 @@ def s.to_sym
     o.delete_field s
     assert_not_respond_to(o, :foo)
     assert_not_respond_to(o, :foo=)
+
+    assert_raise(NameError) { o.delete_field(s) }
+    assert_equal(s.to_sym, o.delete_field(s) { :foo })
+
+    o[s] = :foobar
+    assert_respond_to(o, :foo)
+    assert_respond_to(o, :foo=)
+    assert_equal(:foobar, o.delete_field(s) { :baz })
+
+    assert_equal(42, OpenStruct.new(foo: 42).delete_field(:foo) { :bug })
   end
 
   def test_setter