Groovy: 使用ExpandoMetaClass动态地向类添加方法

//我们将方法rightShift添加到List类。
//实现只是调用List的remove方法
//提供的参数。
List.metaClass.rightShift {
    delegate.remove it
}

def list = ['one', 'two', 'three', 'four']
assert 4 == list.size()

list.rightShift 'two'
assert 3 == list.size()
assert ['one', 'three', 'four'] == list

// Operator overloading in action: rightShift is >>
list >> 'one'
assert 2 == list.size()
assert ['three', 'four'] == list


//我们还可以向特定实例而不是类添加行为。
//注意我们使用实例列表而不是类List来分配
//方法groovy到metaClass属性。
list.metaClass.groovy {
    delegate.collect { it + ' groovy' }
}

assert ['three groovy', 'four groovy'] == list.groovy()

def newList = ['a', 'b']
try {
    newList.groovy()  // groovy method was added to list instance not List class.
    assert false
} catch (e) {
    assert e instanceof MissingMethodException
}