CODEWITHSUNDEEP
scalasyntaxdslsyntactic-sugar
teucer
teucer

Reputation: 6238

method with angle brackets (<>)

Is it possible to have angle brackets in method names , e.g. :

class Foo(ind1:Int,ind2:Int){...}
var v = new Foo(1,2)
v(1) = 3 //updates ind1
v<1> = 4 //updates ind2

The real situation is obviously more complicated than this!!I am trying to provide a convenient user interface.

Upvotes: 14

Views: 2659

Answers (3)

kassens
kassens

Reputation: 4475

This response is not meant to be taken too seriously - just a proof that this can almost be achieved using some hacks.

class Vector(values: Int*) {
  val data = values.toArray
  def < (i:Int) = new {
    def `>_=`(x: Int) {
      data(i) = x
    }
    def > {
      println("value at "+ i +" is "+ data(i))
    }
  }
  override def toString = data.mkString("<", ", ", ">")
}

val v = new Vector(1, 2, 3)
println(v) // prints <1, 2, 3>
v<1> = 10
println(v) // prints <1, 10, 3>
v<1> // prints: value at 1 is 10

Using this class we can have a vector that uses <> instead of () for "read" and write access. The compiler (2.9.0.1) crashes if > returns a value. It might be a bug or a result of misusing >.

Upvotes: 41

Kim Stebel
Kim Stebel

Reputation: 42047

With a little trickery you can actually get quite close to what you want.

object Foo {
  val a:Array[Int] = new Array(100)
  def <(i:Int) = new Updater(a, i)
}

class Updater(a:Array[Int], i:Int) {
  def update(x:Int) {
    a(i) = x
  }
  def >() = this
}

Foo<1>() = 123

I am not sure why Scala requires the () though. And yes, this is a bit of a hack...

Upvotes: 1

Jean-Philippe Pellet
Jean-Philippe Pellet

Reputation: 59994

Edit: I was wrong; kassens's answer shows how to do it as you want.

It is not possible to implement a method that would be called when you write v<1> = 4 (except, maybe, if you write a compiler plugin?). However, something like this would be possible:

class Foo {
  def at(i: Int) = new Assigner(i)
  class Assigner(i: Int) {
    def :=(v: Int) = println("assigning " + v + " at index " + i)
  }
}

Then:

val f = new Foo
f at 4 := 6

Upvotes: 6

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