Scala：布尔到选项
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Scala: Boolean to Option
提问by Chris Beach
I have a Boolean and would like to avoid this pattern:
我有一个布尔值，想避免这种模式：
if (myBool)
Option(someResult)
else
None
What I'd like to do is
我想做的是
myBool.toOption(someResult)
Any suggestions with a code example would be much appreciated.
任何有关代码示例的建议将不胜感激。
采纳答案by Xavier Guihot
Starting Scala 2.13, Optionhas a whenbuilder for this exact purpose:
开始Scala 2.13,Option具有when用于此确切目的的构建器：
Option.when(condition)(result)
For instance:
例如：
Option.when(true)(3)
// Option[Int] = Some(3)
Option.when(false)(3)
// Option[Int] = None
Also note Option.unlesswhich promotes the opposite condition.
还要注意Option.unless哪个促进了相反的条件。
回答by n1r3
Scalaz has a way to do it with BooleanOps.option. That would allow you to write :
Scalaz 有一种方法可以使用BooleanOps.option来做到这一点。这将允许你写：
myBool.option(someResult)
If you don't want to add a Scalaz dependency, just add the following in your code :
如果您不想添加 Scalaz 依赖项，只需在代码中添加以下内容：
implicit class RichBoolean(val b: Boolean) extends AnyVal {
final def option[A](a: => A): Option[A] = if (b) Some(a) else None
}
回答by Brian O'Clair
Option().collect() is a good pattern for this kind of thing.
Option().collect() 是处理这类事情的好模式。
Option(myBool).collect { case true => someResult }
from the REPL:
来自 REPL：
scala> (Option(true).collect { case true => 3 }, Option(false).collect { case true => 3 })
res3: (Option[Int], Option[Int]) = (Some(3),None)
回答by jazmit
None of the other answers answer the question as stated! To get the exact semantics you specified use:
其他答案都没有回答所述问题！要获得您指定的确切语义，请使用：
implicit class BoolToOption(val self: Boolean) extends AnyVal {
def toOption[A](value: => A): Option[A] =
if (self) Some(value) else None
}
You can then write
然后你可以写
myBool.toOption(someResult)
eg:
例如：
scala> true.toOption("hi")
res5: Option[String] = Some(hi)
scala> false.toOption("hi")
res6: Option[String] = None
回答by jazmit
If you don't mind someResultbeing evaluated no matter the value of myBoolyou can also use
如果你不介意someResult被评价不管myBool你的价值你也可以使用
Some(someResult).filter(myBool)
回答by J Cracknell
Another choice:
另一种选择：
implicit class RichOptionCompanion(val self: Option.type) extends AnyVal {
def when[A](cond: Boolean)(value: => A): Option[A] = if(cond) Some(value) else None
}
Usage:
用法：
Option.when(foo != "bar") { ... }
回答by kiritsuku
scala> PartialFunction.condOpt(5) { case x if true => x }
res9: Option[Int] = Some(5)
scala> PartialFunction.condOpt(5) { case x if false => x }
res10: Option[Int] = None
Here, the guard holds the condition and the value passed to condOptis the value returned if the guard evaluates to true.
这里，守卫保存条件，传递给condOpt的值是当守卫评估为真时返回的值。
回答by flavian
class RichBool[T](a: Boolean, res:=> T) {
def toOption: Option[T] = if (a) Some(res) else None
}
implicit def boolToRichBool[T](tp: (Boolean, T)): RichBool[T] = new RichBool(tp._1, tp._2);
This would give you:
这会给你：
(true, 5).toOption // Some(5);
(false, 3).toOption // None
回答by Joe
Here are a couple things I would consider:
我会考虑以下几点：
val bool: Boolean = ???
val result = 1337
Option(bool).withFilter(identity).map(_ => result)
or
或者
for {
opt <- Option(bool)
if opt
} yield result
回答by Gal Morad
Option(true).find(_ == true) // Some(true)
Option(false).find(_ == true) // None
