OOPs在这个任务中发生了什么

Question

我遇到了这些代码

ClassA classAObject;
//some lines of code that hydrate 'classAObject'
DerivedFromClassA derivedObject = classAObject as DerivedFromClassA;

最后一行是怎么回事？它是仅为derivedObject赋予在derivedObject和classAObject之间共同的那些值吗？

Answer 1

不,它大致相当于:

DerivedFromClassA derivedObject = null;
if (classAObject is DerivedFromClassA)
{
    derivedObject = (DerivedFromClassA) classAObject;
}

换句话说,结果将是空引用或对同一对象的引用,但静态类型为派生类型.