Implement a method using a function value in Scala

Question

Is it possible to provide an implementation of a method using a function object/value? I would like to write something in the spirit of:

abstract class A { def f(x:Int) : Int }

class B extends A { f = identity }

deamon · Accepted Answer · 2010-01-23 21:42:57Z

7

You can use a field of type function like this:

abstract class A { val f: (Int) => Int}

val identity = (x: Int) => x*x

class B extends A { override val f = identity }

answered Jan 23, 2010 at 21:42

deamon

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2 Comments

Michał Bendowski Over a year ago

And is there a difference between a method and a value like this? (P.S. identity is already define id Predef, and I don't want it to square the argument ;)

Randall Schulz Over a year ago

Methods in Scala are not first-class entities. Values are. Functions are values (functions have to be first-class for just about any definition of a functional language). Methods are lifted to functions through partial application.

Community · Accepted Answer · 2017-05-23 10:33:01Z

3

Just to complement deamon's answer, here's one alternate example:

abstract class A { val f: (Int) => Int }
class B extends A { val f: (Int) => Int = identity _ }

edited May 23, 2017 at 10:33

CommunityBot

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answered Jan 24, 2010 at 0:51

Daniel C. Sobral

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Comments

Community · Accepted Answer · 2017-05-23 12:10:51Z

1

And to complement deamon and Daniel, here's another:

abstract class A { def f: (Int)=>Int }
class B extends A { val f = identity _ }
class C extends A { def f = identity _ }
class D extends A { def f = (x:Int) => -x }

If you are stuck with a normal def, then the best you can do is

abstract class Z { def f(x:Int):Int }
class Y extends Z { def f(x:Int) = identity(x) }

edited May 23, 2017 at 12:10

CommunityBot

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answered Jan 24, 2010 at 23:20

Rex Kerr

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