CODEWITHSUNDEEP
scala
user79074
user79074

Reputation: 5270

How to reference object from scala high order method

I'm wondering is there a way to access the object which a high order method is called from in scala. For example say I have the following code:

val list = List(1, 3, 4, -1, 2, 0)
val filtered = list filter(_ > 0)

Say within the filter method I wanted to test the head value how would I achieve it? Something like:

val filter = list filter(_ > 0 + head)

Upvotes: 0

Views: 90

Answers (2)

joescii
joescii

Reputation: 6533

You access it the same way you did when you accessed filter:

val filter = list filter(_ > 0 + list.head)

I should mention that since List is immutable, you can do this safely.

If you are chaining multiple operations on the list, then the simplest solution is to create an intermediate val:

val first10 = x.getList() take 10
val filter = first10 filter(_ > 0 + first10.head)

As much as I love chaining operations together, this can often be more readable anyway.

Upvotes: 8

Giorgos Keramidas
Giorgos Keramidas

Reputation: 1848

You can always pass the result of getList to a function e.g.:

scala> def getList: List[Int] = (0 to 10).toList
getList: List[Int]

scala> getList match { case (xs: List[Int]) =>
     |   xs.filter(_ > xs.head + 5)
     | }
res1: List[Int] = List(6, 7, 8, 9, 10)

or something slightly more interesting than x > 5:

scala> def getList: List[Int] = (10 to 1 by -1).toList
getList: List[Int]

scala> getList
res6: List[Int] = List(10, 9, 8, 7, 6, 5, 4, 3, 2, 1)

scala> getList match { case (xs: List[Int]) =>
     |   xs.filter{ x => xs.head % x == 0 }
     | }
res7: List[Int] = List(10, 5, 2, 1)

Note: This works fine for xs.head, since it should be a pretty cheap operation, but if you plan looking further down into the list, like xs(5) or something, you would be traversing the list many many times.

Upvotes: 0

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