Cast collection to array before merge

Fix #205

lib/jbuilder.rb

@@ -174,12 +174,14 @@ def child!
   #
   #   [1,2,3]
   def array!(collection = [], *attributes, &block)
-    array = if block
+    array = if collection.nil?
+      []
+    elsif block
       _map_collection(collection, &block)
     elsif attributes.any?
       _map_collection(collection) { |element| extract! element, *attributes }
     else
-      collection
+      collection.to_a
     end
 
     merge! array
@@ -276,8 +278,6 @@ def _set_value(key, value)
   end
 
   def _map_collection(collection)
-    return [] if collection.nil?
-
     collection.map do |element|
       _scope{ yield element }
     end

test/jbuilder_test.rb

@@ -18,6 +18,16 @@ def map(&block)
   end
 end
 
+class VeryBasicWrapper < BasicObject
+  def initialize(thing)
+    @thing = thing
+  end
+
+  def method_missing(name, *args, &block)
+    @thing.send name, *args, &block
+  end
+end
+
 # This is not Struct, because structs are Enumerable
 class Person
   attr_reader :name, :age
@@ -254,6 +264,16 @@ class JbuilderTest < ActiveSupport::TestCase
     assert_equal 'world', result['comments'].second['content']
   end
 
+  test 'array! casts array-like objects to array before merging' do
+    wrapped_array = VeryBasicWrapper.new(%w[foo bar])
+
+    result = jbuild do |json|
+      json.array! wrapped_array
+    end
+
+    assert_equal %w[foo bar], result
+  end
+
   test 'nesting multiple children from array with inline loop on root' do
     comments = [ Comment.new('hello', 1), Comment.new('world', 2) ]