今天在写Swift代码的时候,写到把对象存进数组并计算数组里每个类型对象的个数时:(以下为)
<span style="font-size:18px;">class Person:{ } class Teacher:Person{ } class Student:Person{ } var person = Person() var teacher = Teacher() var student1 = Student() var student2 = Student() var arr = [teacher,student1,student2,person] var statistic:[String: Int]=["person" : 0,"teacher" : 0,"student" : 0]</span>
使用了is比较类型:
<span style="font-size:18px;">for st in arr{ if st is Person{ statistic["person"]! = statistic["person"]!+1 }else if st is Student{ statistic["student"]! = statistic["student"]!+1 }else if st is Teacher{ statistic["teacher"]! = statistic["teacher"]!+1 } }</span>
结果出现了
warning: 'is' test is always true 发现代码没有问题啊,于是就找了半天的bug,终于,大半个小时候,找到了原因:
因为Student类和Teacher类都继承于Person,所以is就把他俩都认为是Person类,于是就在
<span style="font-size:18px;">if st is Person这里恒为真,于是就不能正常进行类型判断。这应该算是一个Swift的漏洞吧,is做得还不够完善。</span>
<span style="font-size:18px;">解决方法是吧父类的Person的比较写在最后:</span>
<span style="font-size:18px;"><pre name="code" class="objc">for st in arr{ if st is Teacher{ statistic["teacher"]! = statistic["teacher"]!+1 }else if st is Student{ statistic["student"]! = statistic["student"]!+1 }else if st is Person{ statistic["person"]! = statistic["person"]!+1 } }</span>
<span style="font-size:18px;">这样就可以正常进行分类了。。。。。。。</span>