[英]Empty array can be cast to array of any type
It seems empty arrays in Swift can be cast to any array type. 似乎Swift中的空数组可以强制转换为任何数组类型。
See the following example: 请参见以下示例:
var obj = [Int]()
// compiler warns that this cast always fails, but this evaluates to true
print(obj is [String])
obj.append(3)
// This evaluates to false as expected
print(obj is [String])
This is easily verifiable in a playground, but will also happen in compiled code. 这在操场上很容易验证,但是也会在编译后的代码中发生。 Is this a known issue? 这是一个已知的问题?
As @Hamish indicated, this is indeed a known issue. 正如@Hamish指出的,这确实是一个已知问题。 His comment points to bug report https://bugs.swift.org/browse/SR-6192 . 他的评论指向错误报告https://bugs.swift.org/browse/SR-6192 。
A workaround for this type logic seems to be 这种逻辑的解决方法似乎是
type(of: obj) == [SomeType].self
To expand on the example above, 为了扩展上面的示例,
var obj = [Int]()
obj is [String] // true
type(of: obj) == [String].self // false
type(of: obj) == [Int].self // true
obj.append(3)
obj is [String] // false
type(of: obj) == [String].self // false
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