消除可选链

Question

这是不允许的(坏表达)

if !(let nsDictionaryObject = swiftObject as? NSDictionary)
{
    "Error could not make NSDictionary in \(self)"
    return
}

是否可以在1行中检查可选链表达式的否定值？

Answer 1

在Swift 2.0中,您可以使用

guard let nsDictionaryObject = swiftObject as? NSDictionary else {
    "Error could not make NSDictionary in \(self)"
    return
}

这也将绑定nsDictionaryObject到guard语句之外的范围.