复合类型可以由多个对象类型构成，主要用于缩短已有对象成员的签名。 <br/> **语法：** ```scala A with B with C with ... ``` ```scala object App{ def main(args: Array[String]): Unit = { trait X1 trait X2 trait X3 // 定义复合类型参数x def test(x: X1 with X2 with X3): Unit = { println("OK") } // 函数调用，实参为匿名对象 test(new X1 with X2 with X3) // OK object A extends X1 with X2 with X3 // 函数调用，实参为单例对象 test(A) // OK } } ```