diff --git a/16_interfaces/casting.v b/16_interfaces/casting.v
index 7b4c443..79398f1 100644
--- a/16_interfaces/casting.v
+++ b/16_interfaces/casting.v
@@ -2,21 +2,19 @@
 
 struct Dog{
 	breed string
-	speak() string
 }
 
-fn (d Dog) speak() string {
-	println('Woof')
+fn (d Dog) speak() string{
+	return 'Woof'
 }
 
 
 struct Cat{
 	breed string
-	speak() string
 }
 
 fn (c Cat) speak() string{
-	println('Meow')
+	return 'Meow'
 }
 
 interface Something{}
@@ -24,7 +22,7 @@ interface Something{}
 
 fn announce(s Something){
 	if s is Dog {
-		println('a ${s.breed] dog')
+		println('a ${s.breed} dog')
 	}else if s is Cat{
 		println('a cat speaks ${s.speak()}')
 	}else {
diff --git a/16_interfaces/interface_example4.v b/16_interfaces/interface_example4.v
new file mode 100644
index 0000000..91b71e1
--- /dev/null
+++ b/16_interfaces/interface_example4.v
@@ -0,0 +1,36 @@
+interface IFoo{
+	foo()
+}
+
+interface IBar{
+	bar()
+}
+
+struct SFoo{}
+
+fn (sf SFoo) foo() {}
+
+
+struct SFooBar {}
+
+fn (sfb SFooBar) foo() {}
+
+
+fn (sfb SFooBar) bar() {
+	dump('This implements IBar')
+}
+
+fn main(){
+
+	mut arr := []IFoo{}
+	arr << SFoo{}
+	arr << SFooBar{}
+
+	for a in arr{
+		dump(a)
+	
+		if a is IBar{
+			a.bar()
+		}
+	}
+}
\ No newline at end of file