gistfile1.scala

➜ scala
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scala> val extractor: Int => Option[Int] = { i => println("checking i = %d".format(i)); if (i == 10) Some(i) else None }
extractor: Int => Option[Int] = <function1>

scala> val seq = Seq.range(1,1000000)
seq: Seq[Int] = List(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177,...

// CALLED TWICE HERE
scala> seq.collectFirst(Function.unlift(extractor))
checking i = 1
checking i = 2
checking i = 3
checking i = 4
checking i = 5
checking i = 6
checking i = 7
checking i = 8
checking i = 9
checking i = 10
checking i = 10
res0: Option[Int] = Some(10)

// CALLED ONCE HERE
scala> seq.view.map(extractor).collectFirst { case Some(v) => v }
checking i = 1
checking i = 2
checking i = 3
checking i = 4
checking i = 5
checking i = 6
checking i = 7
checking i = 8
checking i = 9
checking i = 10
res6: Option[Int] = Some(10)