CODEWITHSUNDEEP
scalaoperator-overloadingoperators
user2887596
user2887596

Reputation: 643

Scala custom operator (example abs)

I know that scala allows overloading for it's default operators (+, - ! etc.) . Is it possible to define custom operators and make something like the |.| operator so that | -3| that evaluates to 3. Or defining an operator like ++++ so that a ++++ b equals a+3*b?

Upvotes: 3

Views: 4846

Answers (2)

Nazarii Bardiuk
Nazarii Bardiuk

Reputation: 4342

An example to extend @assaf-mendelson answer

case class Abs(a: Int) {
  def !(): Int = a.abs
}

implicit def toAbs(a: Int) = new {
  def unary_! : Abs = Abs(a)
}

then 

> val a = -3
a: Int = -3

> !a
res0: Abs = Abs(-3)

> !a!
res1: Int = 3

> val b = 12
b: Int = 12

> !b!
res2: Int = 12

> (!a!) + (!b!)
res3: Int = 15

We cannot implement abs as |a| because unary_ works only with !, ~, + and -

Upvotes: 1

Assaf Mendelson
Assaf Mendelson

Reputation: 12991

You should look at scala operators documentation.

You can easily make the ++++ operator but not the |.| operator.

Operators in scala are just functions with non alphanumeric name. Since scala also support call a.f(b) as a f b then you can achieve the first behavior. For example:

case class A(v: Int) {
  def ++++(b: A): A = A(v + 3 * b.v)
}

val a = A(1)
val b = A(2)
a ++++ b
>> A(7)
a.++++(b) // just another way of doing the exact same call

If you want to add this to integer you would simply create an implicit class to add it.

Another option is to prefix the operator for example consider doing -a to get the negative. There is no "first element" to apply the - to, instead - is applied to a (see this answer).

For example:

case class A(v: Int) {
  def unary_!(): Int = -v
}
val a = A(3)
!a
>> -3

Doing |.| has two issues: First there are two parts to the operator, i.e. it is split. The second is the use of |

In order to do a two part operator (say !.!) you would probably want to generate some private type and return it from one ! and then use it as the input for the other to return the output type.

The second issue is the use of | which is an illegal character. Look at this answer for a list of legal characters

Upvotes: 6

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