implement builtin swap

src/ruby/ycp/builtins.rb

@@ -332,8 +332,20 @@ def self.reduce *params, &block
 
 
       # Creates new list with swaped elemetns at offset i1 and i2.
-      def self.swap
-        raise "Builtin list::swap() is not implemented yet"
+      def self.swap list, offset1, offset2
+        return nil if list.nil? || offset1.nil? || offset2.nil?
+
+        return list if offset1 < 0 || offset2 >= list.size || (offset1 > offset2)
+
+        res = []
+        if offset1 > 0
+          res.concat list[0..offset1-1]
+        end
+        res.concat list[offset1..offset2].reverse!
+        if offset2 < list.size-1
+          res.concat list[offset2+1..-1]
+        end
+        return res
       end
     end
 

tests/ruby/builtins_test.rb

@@ -550,4 +550,25 @@ def test_list_reduce_2params
     assert_equal 5, YCP::Builtins::List.reduce(5,[]) { |x,y| next x }
     assert_equal nil, YCP::Builtins::List.reduce(nil,nil) { |x,y| next x }
   end
+
+  SWAP_TESTDATA = [
+    [nil,nil,nil,nil],
+    [[0],nil,0,nil],
+    [[0],0,nil,nil],
+    [[0],0,nil,nil],
+    [[5,6],-1,1,[5,6]],
+    [[5,6],0,2,[5,6]],
+    [[0,1,2,3],0,3,[3,2,1,0]],
+    [[0,1,2,3],0,2,[2,1,0,3]],
+    [[0,1,2,3],1,3,[0,3,2,1]],
+    [[0,1,2,3],2,2,[0,1,2,3]],
+  ]
+  def test_list_swap
+    SWAP_TESTDATA.each do |list,offset1,offset2,result|
+      list_prev = list.nil? ? nil : list.dup 
+      assert_equal result, YCP::Builtins::List.swap(list, offset1, offset2)
+      #check that list is not modified
+      assert_equal list_prev, list
+    end
+  end
 end