问题描述
问题:
在带有swift 2.2的Xcode 7.3下运行以下代码时,编译器无法正确推断可选类型:
When running the following code under Xcode 7.3 with swift 2.2, the compiler is unable to correctly infer the type of the optional:
import Foundation
func whatAmI<T>(inout property:T?)
{
switch property {
case is Int?:
print("I am an Int?")
case is String?:
print("I am a String?")
default:
print("I don't know what I am")
}
}
var string : String?
whatAmI(&string)
在我的Xcode 7.3上,这将打印I am an Int?
On my side with Xcode 7.3 this will print I am an Int?
但是,当我在将变量传递给函数之前用空字符串初始化变量时,开关将其推断为字符串吗?.
However, when I initialize the variable with an empty string before passing it to the function, the switch infers it to be a String?.
这将在以前的Xcode版本中打印I am a String?
.
This would print I am a String?
in the previous Xcode version.
您得到类似的结果吗?
观察:
使用此功能签名时会发生同样的情况:
The same occurs when using this function signature:
func whatAmI(property:AnyObject?)
-错误-
此问题是Swift 2.2中的回归: https://bugs.swift.org/browse/SR-1024
This issue is a regression in swift 2.2:https://bugs.swift.org/browse/SR-1024
推荐答案
这似乎是一个错误.最小的示例如下:
This seems to be a bug. The minimal example is the following:
func genericMethod<T>(property: T?) {
print(T) // String
let stringNil = Optional<String>.None
print(stringNil is String?) // true (warning - always true)
print(stringNil is T?) // true
let intNil = Optional<Int>.None
print(intNil is String?) // false (warning - always fails)
print(intNil is T?) // true - BUG
}
genericMethod("")
这篇关于在Swift 2.2中无法正确推断出可选类型的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!