Unless

Use case

Unless is simply the inverse of if. There is also an alias available, if you’re not too comfortable with “unless”, you can use “ifNot”. That’s the boring use case, and surely, not always recommended - just use if.

The nicer usecase comes with the implicit on String and AnyRef for which you can “return the given value unless something” (for strings “” will be returned, for other values None).

Unless for strings

import UnlessWord._

val itIsALie = false
val msg = "the cake is %sa lie.".format("NOT ".unless(itIsALie))
assert { msg == "the cake is NOT a lie." }

Unless instead of if

Unless can be used as simple replacemet for if(!test):

import UnlessWord._

val result: Option[String] = unless (false) {
  "It"
}

result should equal (Some("It"))

As it returns an option, you can use the following idiom to implement something like an “else”:

// when
val it = unless (true) {
  "Value"
} orElse {
  Some("Else")
}

// then
it should equal (Some("Else"))

Although personally I would discurrage using this construct, in favor of a plain if. Take a look at using blocks with unless, more “ruby style” to see it shine a bit more.

Unless on values

On other values, it will generate an option, depenting on wether the condition was met or not.

// given
val value = 12345
val errorsOccurred = true

// when
val got = value unless errorsOccurred

// then
got should equal (None)

// given
val value = 200
val errorsOccurred = false

// when
val got = value unless errorsOccurred

// then
got should equal (Some(200))

Unless on code blocks

Using this trick, you may use UnlessWord just like you would the Ruby unless modifier syntax.

import Unless._

{ logger.error("We had some errors!") } unless computationWentFine
{ logger.error("We had some errors!") } ifNot computationWentFine

The above code will execute only if the computationWentFine value is false. This syntax may sometimes seem a bit misleading, so use it with caution.

Such code block, returns the value returned by the block, but obviously wrapped in an Option, as it may not have been executed at all:

import Unless._

val noErrorsFound = true
val value: Option[String] = { "Errors!" } unless noErrorsFound

value should equal (None)