scala，从 Some(value) 获取值
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scala, get values from Some(value)
提问by M.Hell
i am currently trying to read myself into scala. But i got stuck on the following:
我目前正在尝试将自己读入 Scala。但我陷入了以下问题：
val value: String = properties(j).attribute("value").toString
print(value)
The xml property is read and converted to a string, but gets viewed as "Some(value)". I have tried several things but none seems to work when not i myself created the value with "Option: String"(which was the common solution). Does somebody know an easy way to get rid of the "Some("?
xml 属性被读取并转换为字符串，但被视为“Some(value)”。我已经尝试了几件事，但似乎没有一个工作，当我自己用“选项：字符串”（这是常见的解决方案）创建值时。有人知道摆脱“Some(”的简单方法吗？
Greetings Ma
问候马
回答by M.Olmsted
The value you're calling the toString method on is an Option[String]type, as opposed to a plain String. When there is a value, you'll get Some(value), while if there's not a value, you'll get None.
您调用 toString 方法的值是一种Option[String]类型，而不是普通的String. 当有值时，你会得到Some(value)，而如果没有值，你会得到None。
Because of that, you need to handle the two possible cases you may get back. Usually that's done with a match:
因此，您需要处理可能返回的两种情况。通常这是通过匹配完成的：
val value: String = properties(j).attribute("value") match {
case None => ""//Or handle the lack of a value another way: throw an error, etc.
case Some(s: String) => s //return the string to set your value
}
回答by sumeet agrawal
You can apply get method on Some(value)
您可以在 Some(value) 上应用 get 方法
object Example {
def main(args: Array[String]) = {
val vanillaDonut: Donut = Donut("Vanilla", 1.50)
val vanillaDonut1: Donut = Donut("ChocoBar", 1.50,Some(1238L))
println(vanillaDonut.name)
println(vanillaDonut.productCode)
println(vanillaDonut1.name)
println(vanillaDonut1.productCode.get)
}
}
case class Donut(name: String, price: Double, productCode: Option[Long] = None)
Result:- Vanilla
结果：-香草
None
没有任何
ChocoBar
巧克力吧
1238
1238
回答by Nan Li
"Some().get" could return the real value. For example:
"Some().get" 可以返回实际值。例如：
val m = Map(("1", 2), (3, 4));
val a = m.get("1");
println(a.get + 1);
回答by M.Hell
Hi and thanks for the input.
I took your code with minor changes, and it was quite confusing with the variables node.seq, String, Some(String), Some[A]in the beginning. It works now quite fine with this short version:
嗨，感谢您的投入。我把你的代码做了一些小的改动，node.seq, String, Some(String), Some[A]一开始的变量很混乱。它现在可以很好地使用这个简短版本：
val value = properties(j).attribute("value") match {
case None => ""
case Some(s) => s //return the string to set your value
}
