I can write the code like this:
str match {
case s if s.startsWith("!!!") => s.stripPrefix("!!!")
case _ =>
}
But I want to know is there any better solutions. For example:
str match {
case "!!!" + rest => rest
case _ =>
}
val r = """^!!!(.*)""".r
val r(suffix) = "!!!rest of string"
So suffix will be populated with rest of string, or a scala.MatchError gets thrown.
A different variant would be:
val r = """^(!!!){0,1}(.*)""".r
val r(prefix,suffix) = ...
And prefix will either match the !!! or be null. e.g.
(prefix, suffix) match {
case(null, s) => "No prefix"
case _ => "Prefix"
}
The above is a little more complex than you might need, but it's worth looking at the power of Scala's regexp integration.
Starting Scala 2.13, it's now possible to pattern match a String by unapplying a string interpolator:
"!!!hello" match {
case s"!!!$rest" => rest
case _ => "oups"
}
// "hello"
If it's the sort of thing you do often, it's probably worth creating an extractor
object BangBangBangString{
def unapply(str:String):Option[String]= {
str match {
case s if s.startsWith("!!!") => Some(s.stripPrefix("!!!"))
case _ => None
}
}
}
Then you can use the extractor as follows
str match{
case BangBangBangString(rest) => println(rest)
case _ => println("Doesn't start with !!!")
}
or even
for(BangBangBangString(rest)<-myStringList){
println("rest")
}
Good question !
Even i was trying a lot to find out the answer.
Here is a good link where I found the answer
object _04MatchExpression_PatternGuards {
def main(args: Array[String]): Unit = {
val url: String = "Jan";
val monthType = url match {
case url if url.endsWith(".org") => "Educational Websites";
case url if url.endsWith(".com") => "Commercial Websites";
case url if url.endsWith(".co.in") => "Indian Websites"
case _ => "Unknow Input";
}
}
}
Related
I want to avoid Runtime undefined behaivors as follows:
val jsonExample = Json.toJson(0)
jsonExample.asOpt[Instant]
yield Some(1970-01-01T00:00:00Z)
How can I verify this using partial function with a lift or some other way, to check thatits indeed Instant, or how you recommend to validate?
ex1:
val jsonExample = Json.toJson(Instant.now())
jsonExample match { ... }
ex2:
val jsonExample = Json.toJson(0)
jsonExample match { ... }
Examples for desired output:
validateInstant(Json.toJson(Instant.now())) -> return Some(...)
validateInstant(Json.toJson(0)) -> return None
I can do somthing as follows, maybe some other ideas?
Just wanted to add a note regarding parsing json, there some runtime undefined problems when we are trying to parse .asOpt[T]
for example:
Json.toJson("0").asOpt[BigDecimal] // yields Some(0)
Json.toJson(0).asOpt[Instant] // yields Some(1970-01-01T00:00:00Z)
We can validate it as follows or some other way:
Json.toJson("0") match {
case JsString(value) => Some(value)
case _ => None
}
Json.toJson(0) match {
case JsNumber(value) => Some(value)
case _ => None
}
Json.toJson(Instant.now()) match {
case o # JsString(_) => o.asOpt[Instant]
case _ => None
}
You can use Option:
def filterNumbers[T](value: T)(implicit tjs: Writes[T]): Option[Instant] = {
Option(Json.toJson(value)).filter(_.asOpt[JsNumber].isEmpty).flatMap(_.asOpt[Instant])
}
Then the following:
println(filterNumbers(Instant.now()))
println(filterNumbers(0))
will output:
Some(2021-02-22T10:35:13.777Z)
None
I have a few vals that match for matching values
Here is an example:
val job_ = Try(jobId.toInt) match {
case Success(value) => jobs.findById(value).map(_.id)
.getOrElse( Left(WrongValue("jobId", s"$value is not a valid job id")))
case Failure(_) => jobs.findByName(jobId.toString).map(_.id)
.getOrElse( Left(WrongValue("jobId", s"'$jobId' is not a known job title.")))
}
// Here the value arrives as a string e.i "yes || no || true || or false" then converted to a boolean
val bool_ = bool.toLowerCase() match {
case "yes" => true
case "no" => false
case "true" => true
case "false" => false
case other => Left(Invalid("bool", s"wrong value received"))
}
Note: invalid case is case class Invalid(x: String, xx: String)
above i'm looking for a given job value and checking whether it exist in the db or not,
No I have a few of these and want to add to a list, here is my list val and flatten it:
val errors = List(..all my vals errors...).flatten // <--- my_list_val (how do I include val bool_ and val job_)
if (errors.isEmpty) { do stuff }
My result should contain errors from val bool_ and val job_
THANK!
You need to fix the types first. The type of bool_ is Any. Which does not give you something you can work with.
If you want to use Either, you need to use it everwhere.
Then, the easiest approach would be to use a for comprehension (I am assuming you're dealing with Either[F, T] here, where WrongValue and Invalid are both sub-classes of F and you're not really interested in the errors).
for {
foundJob <- job_
_ <- bool_
} yield {
// do stuff
}
Note, that in Scala >= 2.13 you can use toIntOption when converting the String to Int:
vaj job_: Either[F, T] = jobId.toIntOption match {
case Some(value) => ...
case _ => ...
}
Also, in case expressions, you can use alternatives when you have the same statement for several cases:
val bool_: Either[F, Boolean] = bool.toLowerCase() match {
case "yes" | "true" => Right(true)
case "no" | "false" => Right(false)
case other => Left(Invalid("bool", "wrong value received"))
}
So, according to your question, and your comments, these are the types you're dealing with.
type ID = Long //whatever id is
def WrongValue(x: String, xx: String) :String = "?-?-?"
case class Invalid(x: String, xx: String)
Now let's create a couple of error values.
val job_ :Either[String,ID] = Left(WrongValue("x","xx"))
val bool_ :Either[Invalid,Boolean] = Left(Invalid("x","xx"))
To combine and report them you might do something like this.
val errors :List[String] =
List(job_, bool_).flatMap(_.swap.toOption.map(_.toString))
println(errors.mkString(" & "))
//?-?-? & Invalid(x,xx)
After checking types as #cbley explained. You can just do a filter operation with pattern matching on your list:
val error = List(// your variables ).filter(_ match{
case Left(_) => true
case _ => false
})
Please suggest best was to implement the below code:
Requirement: pass single string or no parameters
object Twofer {
def twofer(name: String*): String = name match {
case Seq(nm) => s"One for $nm, one for me."
case List() => "One for you, one for me."
}
}
Maybe something similar to the following:
def twofer(names: String*): String = List(names: _*) match {
case Nil => "No names!"
case n :: Nil => s"Single name $n"
case ls => s"Multiple names $ls"
}
I'm trying to match case against a String and have the following code:
val selectedAnswers: List[Int] = questionType match {
case "CHECK_BOX" => {
answerCheckBox match {
case Some(answers) => answers
case None => List()
}
}
case "RADIO_BUTTON" => {
answerRadio match {
case Some(answer) => List(answer)
case None => List()
}
}
case _ => {
List()
}
}
Why is it not falling through the _ case when the String is not RADIO_BUTTON or CHECK_BOX?
The values for answerRadio and answerCheckbox are actually coming from the form that I'm submitting to the controller.
val (currentQuesId, questionType, answerRadio, answerCheckBox) = runExamForm.bindFromRequest.get
And the form declaration looks like:
val runExamForm = Form(
tuple(
"currentQuestionId" -> number,
"questionType" -> text,
"answerRadio" -> optional(number),
"answerCheckbox" -> optional(list(number))
)
)
This is "equivalent" version of your code:
val selectedAnswers: List[Int] = questionType match {
case "CHECK_BOX" => answerCheckBox.toList.flatten
case "RADIO_BUTTON" => answerRadio.toList
case _ => List()
}
Does it work as expected?
It's a long shot, but try replacing the _ with some other name (x is fine) and make sure that your code contains nothing but regular whitespace.
Very rarely I've seen bizarre errors like this caused by other non-printing characters in the code, which always seemed to be caused by pasting code from a chat on the OSX Skype client.
Also... Can you confirm in your code sample which line the MatchError occurs on?
I am trying to do something like the following:
list.foreach {x =>
x match {
case """TEST: .*""" => println( "TEST" )
case """OXF.*""" => println("XXX")
case _ => println("NO MATCHING")
}
}
The idea is to use it like groovy switch case regex match. But I can't seem to get to to compile. Whats the right way to do it in scala?
You could either match on a precompiled regular expression (as in the first case below), or add an if
clause. Note that you typically don't want to recompile the same regular expression on each case evaluation, but rather have it on an object.
val list = List("Not a match", "TEST: yes", "OXFORD")
val testRegex = """TEST: .*""".r
list.foreach { x =>
x match {
case testRegex() => println( "TEST" )
case s if s.matches("""OXF.*""") => println("XXX")
case _ => println("NO MATCHING")
}
}
See more information here and some background here.
Starting Scala 2.13, it's possible to directly pattern match a String by unapplying a string interpolator:
// val examples = List("Not a match", "TEST: yes", "OXFORD")
examples.map {
case s"TEST: $x" => x
case s"OXF$x" => x
case _ => ""
}
// List[String] = List("", "yes", "ORD")