How to Implement Implicit Conversion to Iterable<T>?

1

I have a BufferedImage for which I wish to implement an Iterable so that I may iterate over all the pixels. 

data class Pixel(val point: Point, val color: Color)



fun BufferedImage.iterable(): Iterable<Pixel> {

  return object: Iterable<Pixel> {

  override fun iterator(): Iterator<Pixel> {

            return iterator()

  }

  }

}


fun BufferedImage.iterator(): Iterator<Pixel> {

  return object : Iterator<Pixel> {

  var currentX = 0

  var currentY = 0


  &nbsp;&nbsp;override fun hasNext(): Boolean {



            return currentY != getHeight()

  }


  &nbsp;&nbsp;override fun next(): Pixel {



            val point = Point(currentX, currentY)

            val color = Color(getRGB(currentX, currentY))


            if (currentX == getWidth() - 1) {

                currentX = 0

                currentY += 1

            } else {

                currentX += 1

            }


            return Pixel(point, color)

  }

  }

}

This code let's me write 

for (pixel in image) { doStuff(pixel) }

And 

image.iterator().map { doStuff(it) }
image.iterable().map { doStuff(it) }

But I can't directly write 

image.map { doStuff(it) }

Why not? I feel like I'm missing only one more piece and then everything will work as intended.

2

Kotlin does not support implicit conversions, in fact, this is something we are strongly against. The best we can offer for your case is explicitly calling some method/property before calling map(), e.g.: 

image.it.map {...}

where 

val BufferedImage.it: Iterable<Pixel>
    get() = ...
1 Like
3

Small addition, recently something changed and keyword operator is now required for declaration of function iterator() to use it implicitly in for cycles.

operator fun BufferedImage.iterator(): Iterator