检查“Any"值是否为对象 [英] Check if `Any` value is object

问题描述

我惊讶地发现这个条件总是成立的:

I was surprised to find that this condition is always true:

let foo: Any = 4
if let object = foo as? AnyObject {
    print("It's an object.")
    //do something with `object` that requires reference semantics
} else {
    print("It's not an object.")
}

看来，不管foo原来是什么类型，都转换成对应类的实例了.有没有可靠的方法来确定 foo 是否是一个对象?

It seems that no matter what type foo was originally, it is converted to an instance of a corresponding class. Is there a reliable way to determine whether or not foo is an object?

推荐答案

UPDATE

我在下面显示的代码被报告为在发布版本中不起作用.(请参阅下方 Paul Cantrell 的评论.)

UPDATE

The code I have shown below is reported as not working in release build. (Please see Paul Cantrell's comment below.)

对我的就我测试而言"的道歉太有限了.

Apologies for my "as far as I tested" was too limited.

当我找到有关此的更多信息时，我会更新此答案.

I'll update this answer when I find some further info about this.

我不确定我们能否在下一个测试版(或 GM 或已发布版本...)中看到这种行为，但这在 Xcode 8 beta 6 中如您所愿.

I'm not sure we can see this behaviour in the next beta (or GM or Released version...), but this works as you expect in Xcode 8 beta 6.

let foo: Any = 4
if type(of: foo) is AnyClass {
    print("It's an object.")
    let object = foo as AnyObject
    //do something with `object` that requires reference semantics
} else {
    print("It's not an object.") //->It's not an object.
}

class MyClass {}
let bar: Any = MyClass()
if type(of: bar) is AnyClass {
    print("It's an object.") //->It's an object.
    let object = foo as AnyObject
    //do something with `object` that requires reference semantics
} else {
    print("It's not an object.")
}

let baz: Any = Array<AnyObject>()
if type(of: baz) is AnyClass {
    print("It's an object.")
    let object = foo as AnyObject
    //do something with `object` that requires reference semantics
} else {
    print("It's not an object.") //->It's not an object.
}

我无法检查所有可能的情况，因此可能在某些边缘情况下这不起作用.但据我测试，这似乎按预期工作.

I cannot check all possible cases, so there may be some edge cases where this does not work. But as far as I tested, this seems to work as expected.

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