Add fallback block to OpenStruct#delete_field (#1409)

Merged-By: marcandre <github@marc-andre.ca>

lib/ostruct.rb

@@ -326,8 +326,10 @@ class OpenStruct
   end
 
   #
-  # Removes the named field from the object. Returns the value that the field
+  # Removes the named field from the object and returns the value the field
-  # contained if it was defined.
+  # contained if it was defined. You may optionally provide a block. 
+  # If the field is not defined, the result of the block is returned, 
+  # or a NameError is raised if no block was given.
   #
   #   require "ostruct"
   #
@@ -341,6 +343,10 @@ class OpenStruct
   #   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
@@ -348,6 +354,7 @@ class OpenStruct
     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 @@ class TC_OpenStruct < Test::Unit::TestCase
     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 @@ class TC_OpenStruct < Test::Unit::TestCase
     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(:bar, o.delete_field(s) { :bar })
+
+    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