object_setClass 到更大的类
我正在使用 object_setClass(id object, Class cls) 更改某些对象的类。我正在将该类更改为原始类的子类。然后我设置了一些仅在子类上定义的属性，事情似乎工作正常。
我对这有效感到有点惊讶，因为据我所知，object_setClass 不会重新分配对象，它只会更改 isa 指针。如果子类实例比原始类实例大得多（意味着有更多的 ivars），我不知道该对象如何按预期工作。
这是否仅仅因为内存中的对象之间存在大量缓冲内存（由于对齐等原因）而起作用？
这是否可靠，或者在某些情况下会崩溃吗？
I am changing the class of some objects using object_setClass(id object, Class cls). I am changing the class to a subclass of the original class. Then I set some properties that are only defined on the subclass, and things seem to work fine.
I was a bit surprised that this worked, because object_setClass, as far as I understand, doesn't reallocate the object, it only changes the isa pointer. If the subclass instances are considerably larger (meaning having many more ivars) than the original class instances, I don't see how the object can work as expected.
Does this work only because there is a lot of buffer memory between objects in memory (due to alignment etc)?
Is this robust, or could it crash under some circumstances?
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它可能会崩溃。从运行时的源代码中可以看出 这里< /a>，它实际上只是交换了
isa指针。如果您确实想将
isa交换为具有更多 ivars 的子类的isa，您应该使用class_createInstance带有非零的extraBytes。It could crash. As can be seen in the source code of the runtime here, it really just swaps the
isapointer.If you really want to swap the
isato anisaof a subclass with more ivars, you should useclass_createInstancewith nonzeroextraBytes.不要使用更大的子类，而是使用 objc_setAssociatedObject 和 objc_getAssociatedObject 将附加对象动态附加到现有的固定大小对象。
Instead of using a larger subclass, use
objc_setAssociatedObjectandobjc_getAssociatedObjectto attach dynamically additional objects to your existing fixed-size object.