Scala 预期异常片段
我正在尝试模拟常见测试框架（例如 JUnit 或 TestNG）的预期异常行为。
这是我到目前为止可以想到的（有效）：
trait ExpectAsserts
{
self : {
def fail (message : String)
def success (message : String)
} =>
def expect[T](exceptionClass : Class[T])(test : => Unit)
{
try
{
test
fail("exception not thrown")
}
catch
{
case expected : T => success("got exception " + expected)
case other : Exception => fail("expected "+ exceptionClass + " but " + other + " thrown instead.")
}
}
}
object Main extends ExpectAsserts
{
def main (args : Array[String])
{
expect(classOf[ArithmeticException])
{
throw new IllegalArgumentException // this should print an error message.
}
}
def fail (s : String)
{
System.err.println(s)
}
def success(s : String)
{
System.out.println(s)
}
}
该代码片段有一个用于执行代码的 main 方法。我的问题是抛出的异常进入第一个模式匹配语句：
case expected : T
尽管我实际上是说异常必须是 T 类型，即 IllegalArgumentException。
有什么想法吗？
I'm trying to simulate the expected exception behavior of common testing frameworks (e.g. JUnit or TestNG).
Here's what I could come up with so far (working):
trait ExpectAsserts
{
self : {
def fail (message : String)
def success (message : String)
} =>
def expect[T](exceptionClass : Class[T])(test : => Unit)
{
try
{
test
fail("exception not thrown")
}
catch
{
case expected : T => success("got exception " + expected)
case other : Exception => fail("expected "+ exceptionClass + " but " + other + " thrown instead.")
}
}
}
object Main extends ExpectAsserts
{
def main (args : Array[String])
{
expect(classOf[ArithmeticException])
{
throw new IllegalArgumentException // this should print an error message.
}
}
def fail (s : String)
{
System.err.println(s)
}
def success(s : String)
{
System.out.println(s)
}
}
The snippet has a main method that exercises the code. My problem is that the exception thrown enters in the first pattern matching statement:
case expected : T
Although I'm actually saying that the exception has to be of type T, which would be IllegalArgumentException.
Any ideas?
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使用
-unchecked进行编译，您将看到一条警告，指出由于类型擦除，类型测试expected: T将始终返回 true。既然您已经传入了类，您可以使用
Class#isInstance代替。在您的代码中，这看起来像：在一个独立的示例中。这里我们隐式地传递了一个
Manifest[T]，这是一种让编译器传递额外参数来获取类型擦除丢弃的信息的方法：进一步阅读：
Compile with
-uncheckedand you'll see a warning that the type testexpected: Twill always return true, thanks to type erasure.Seeing as you have the class passed in you can use
Class#isInstanceinstead. In your code, that would look like:In a self contained example. Here we pass a
Manifest[T]implicitly, which is a way to get the compiler to pass an extra parameter to obtain the information that type erasure threw away:Further reading: