tcpoly_variance.check

来自「JAVA 语言的函数式编程扩展」· CHECK 代码 · 共 6 行

tcpoly_variance.scala:6: error: error overriding method str in class A of type => m[java.lang.Object];
 method str has incompatible type => m[String]
 override def str: m[String]  = error("foo") // since x in m[x] is invariant, ! m[String] <: m[Object]
              ^
one error found