scala - Pattern matching vs if-else

Question

I'm novice in Scala. Recently I was writing a hobby app and caught myself trying to use pattern matching instead of if-else in many cases.

user.password == enteredPassword match {
  case true => println("User is authenticated")
  case false => println("Entered password is invalid")
}

instead of

if(user.password == enteredPassword)
  println("User is authenticated")
else
  println("Entered password is invalid")

Are these approaches equal? Is one of them more preferrable than another for some reason?

Answer 1

class MatchVsIf {
  def i(b: Boolean) = if (b) 5 else 4
  def m(b: Boolean) = b match { case true => 5; case false => 4 }
}

I'm not sure why you'd want to use the longer and clunkier second version.

scala> :javap -cp MatchVsIf
Compiled from "<console>"
public class MatchVsIf extends java.lang.Object implements scala.ScalaObject{
public int i(boolean);
  Code:
   0:   iload_1
   1:   ifeq    8
   4:   iconst_5
   5:   goto    9
   8:   iconst_4
   9:   ireturn

public int m(boolean);
  Code:
   0:   iload_1
   1:   istore_2
   2:   iload_2
   3:   iconst_1
   4:   if_icmpne   11
   7:   iconst_5
   8:   goto    17
   11:  iload_2
   12:  iconst_0
   13:  if_icmpne   18
   16:  iconst_4
   17:  ireturn
   18:  new #14; //class scala/MatchError
   21:  dup
   22:  iload_2
   23:  invokestatic    #20; //Method scala/runtime/BoxesRunTime.boxToBoolean:(Z)Ljava/lang/Boolean;
   26:  invokespecial   #24; //Method scala/MatchError."<init>":(Ljava/lang/Object;)V
   29:  athrow

And that's a lot more bytecode for the match also. It's fairly efficient even so (there's no boxing unless the match throws an error, which can't happen here), but for compactness and performance one should favor if/else. If the clarity of your code is greatly improved by using match, however, go ahead (except in those rare cases where you know performance is critical, and then you might want to compare the difference).