When
Use case
When should be treated as an extension of the traditional if statement, and as such, it should not be over used when a simple if is enough.
It can however do more than if, like having an automatic else clause for values, turning them into Options or for Strings. Another notable feature is allowing a syntax similiar to Ruby’s if modifier (code if condition).
Note
When and Unless share functionality. All you can do with Unless works with When too. You can think of When like an if statement, and unless like an negated if statement.
When for strings
import WhenWord._
val itIsALie = false
val msg = "the cake is %sa lie.".format("NOT ".when(itIsALie))
assert { msg == "the cake is a lie." }
When on values
On other values, it will generate an option, depenting on wether the condition was met or not.
// given
val value = 12345
val allGreen = true
// when
val got = value when allGreen
// then
got should equal (Some(12345))
// given
val value = 200
val allGreen = false
// when
val got = value when allGreen
// then
got should equal (None)
When on code blocks
Using this trick, you may use WhenWord just like you would use the ruby if modifier (code if something).
import WhenWord._
val noErrors = true
{ logger.info("Uff, no errors found!") } when noErrors
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 WhenWord._
val noErrors = false
val value: Option[String] = { "Errors!" } unless noErrors
value should equal (None)
Contents
