*(id *)((char *)object + ivar_getOffset(ivar)) 和 object_getIvar(object, ivar) 之间有什么区别
ivar_getOffset 返回偏移量 实例变量。
ptrdiff_t ivar_getOffset(Ivar ivar) 讨论 对于实例变量 输入 id 或其他对象类型，调用 object_getIvar 和 object_setIvar 而不是使用此偏移量来访问 直接实例变量数据。
在runtime.h中声明
这是为什么呢？ object_getIvar 对对象类型有什么作用？
编辑：将问题从下标 (void *) 更改为 (id *)。
According the Objective-C runtime reference:
ivar_getOffset
Returns the offset of
an instance variable.ptrdiff_t ivar_getOffset(Ivar ivar)
Discussion For instance variables of
type id or other object types, call
object_getIvar and object_setIvar
instead of using this offset to access
the instance variable data directly.Declared In runtime.h
Why is this? What does object_getIvar do to object types?
EDIT: changed question from subscripting (void *) to (id *).
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在获取 ivar 的值时，这两种方法没有区别。您可以通过查看 Apple 开源 Obj-C 运行时代码。
object_setIvar()的作用不仅仅是分配对象指针的偏移量。小心地调用垃圾收集运行时函数 objc_assign_ivar() 来执行实际的分配。将来可能会为这些功能添加更多魔力；一般来说，您应该在任何给定时间使用可用的最高级别的 API。
There is no difference between those two approaches when it comes to getting the value of the ivar. You can verify this by looking at
object_getIvar()'s implementation in Apple's open-source Obj-C runtime code.object_setIvar()does more than just assign to an offset from the object pointer. It is careful to call through to the garbage-collection runtime functionobjc_assign_ivar()to perform the actual assignment.More magic might be added to either of these functions in future; in general, you should use the highest-level API available at any given time.
也许并不是
object_getIvar做了不同的事情，而是id类型的实例变量或其他对象类型很常见，并且调用ivar_getOffset并附加将结果转换为object的值，然后转换为适当的类型要麻烦得多。请注意，根据 C99 标准中的以下信息（重点是我的），您无法可靠地增加
void *的值：要将指针增加任意数字，可以使用
char *代替。Perhaps it's not that
object_getIvardoes something different, but that instance variables of typeidor other object types are commonplace, and that callingivar_getOffsetand appending the result to the value ofobjectand then casting to the appropriate type is much more cumbersome.Note that you cannot reliably increment the value of a
void *, based on the following information from the C99 standard (emphasis mine):To increment a pointer by an arbitrary number, you can use
char *instead.