Is apply and unapply a constructor in scala -


in java can make constructor using class name. in scala have seen different use of apply , unapply, same constructor in java, in can use apply , unapply constructor

apply() can used factory method (not constructor), , is, not restricted or required so. makes apply() special can "silently" invoked.

class myclass(arg: string) {   def apply(n: int):string = arg*n }  val mc = new myclass("blah") mc.apply(2)  // res0: string = blahblah mc(3)        // res1: string = blahblahblah

you'll see apply() used factory method in companion object.

object myclass {   def apply(s: string): myclass = new myclass(s) } val mc = myclass("bliss")  // call object's apply() method

but, again, that's convenient convention, not requirement.

unapply() (and unapplyseq()) different in "silently" called whenever attempt pattern match on class instance.

class myclass(val arg: string) {} object myclass {   def unapply(x: myclass): option[string] = some(x.arg) } val mc = new myclass("bland") mc match {   case myclass(s) => println(s"got $s")  // output: "got bland"   case _          => println("not") }

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