Help understanding match/case

[Jim Newton]

Can someone explain to me what the vert "|"  is in the second case of this code?  

Also, I didn't realize that "x =>" was a valid notation?  Does it return Unit?

quad match {
  case Fork(nw, ne, sw, se) =>
    val cx = quad.centerX
    val cy = quad.centerY
    val sz = quad.size
    drawRect(cx - sz / 2, cy - sz / 2, sz / 2, nw)
    drawRect(cx - sz / 2, cy, sz / 2, sw)
    drawRect(cx, cy - sz / 2, sz / 2, ne)
    drawRect(cx, cy, sz / 2, se)
    drawQuad(depth + 1, nw)
    drawQuad(depth + 1, ne)
    drawQuad(depth + 1, sw)
    drawQuad(depth + 1, se)
  case Empty(_, _, _) | Leaf(_, _, _, _) =>
    // done
}

[Oliver Ruebenacker]

     Hello,

  The "|" means "or".

  Apparently, if nothing comes after the "=>", it is Unit, just like an empty block {}.

     Best, Oliver

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Oliver Ruebenacker

Senior Software Engineer, Diabetes Portal, Broad Institute

[Lanny Ripple]

See http://scala-lang.org/files/archive/spec/2.11/08-pattern-matching.html#pattern-alternatives

Blocks that return Unit do so by having a () placed at tail position by the compiler.  That's why you can do

    def fun(x: Int): Unit = { x + 1 }

and get a ().  (This can be seen by running `scala -Xprint:-5`)

scala> def fun(x: Int): Unit = { case x if x > 0 => x + 1; case _ => }

[[syntax trees at end of                    parser]] // <console>

package $line4 {

  object $read extends scala.AnyRef {

    // ...

        def fun(x: Int): Unit = <empty> match {

          case (x @ _) if x.$greater(0) => x.$plus(1)

          case _ => ()

        }

      }

    }

  }

}

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