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为真：

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.")
}

看起来无论什么类型 foo 原来，它被转换为相应类的实例。是否有可靠的方法来确定 foo 是否是对象？

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报告为在版本构建中不工作。
（请参阅下面的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.)

对我的对我测试的道歉太有限。

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

当我找到这个答案时，我会更新这个答案。

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

不确定我们可以看到这种行为在下一个测试版（或通用或发布版本...），但这是正如你期望在Xcode 8 beta 6。

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.
}

我不能检查所有可能的情况，所以可能有一些边缘情况不工作。但就我测试，这似乎工作正如预期。

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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