Interesting Scala typing solution, doesn't work in 2.7.7?
- by djc
I'm trying to build some image algebra code that can work with images (basically a linear pixel buffer + dimensions) that have different types for the pixel. To get this to work, I've defined a parametrized Pixel trait with a few methods that should be able to get used with any Pixel subclass. (For now, I'm only interested in operations that work on the same Pixel type.) Here it is:
trait Pixel[T <: Pixel[T]] {
def mul(v: Double): T
def max(v: T): T
def div(v: Double): T
def div(v: T): T
}
Now I define a single Pixel type that has storage based on three doubles (basically RGB 0.0-1.0), I've called it TripleDoublePixel:
class TripleDoublePixel(v: Array[Double]) extends Pixel[TripleDoublePixel] {
var data: Array[Double] = v
def this() = this(Array(0.0, 0.0, 0.0))
def toString(): String = {
"(" + data(0) + ", " + data(1) + ", " + data(2) + ")"
}
def increment(v: TripleDoublePixel) {
data(0) += v.data(0)
data(1) += v.data(1)
data(2) += v.data(2)
}
def mul(v: Double): TripleDoublePixel = {
new TripleDoublePixel(data.map(x => x * v))
}
def div(v: Double): TripleDoublePixel = {
new TripleDoublePixel(data.map(x => x / v))
}
def div(v: TripleDoublePixel): TripleDoublePixel = {
var tmp = new Array[Double](3)
tmp(0) = data(0) / v.data(0)
tmp(1) = data(1) / v.data(1)
tmp(2) = data(2) / v.data(2)
new TripleDoublePixel(tmp)
}
def max(v: TripleDoublePixel): TripleDoublePixel = {
val lv = data(0) * data(0) + data(1) * data(1) + data(2) * data(2)
val vv = v.data(0) * v.data(0) + v.data(1) * v.data(1) + v.data(2) * v.data(2)
if (lv > vv) (this) else v
}
}
Now I want to write code to use this, that doesn't have to know what type the pixels are. For example:
def idiv[T](a: Image[T], b: Image[T]) {
for (i <- 0 until a.data.size) {
a.data(i) = a.data(i).div(b.data(i))
}
}
Unfortunately, this doesn't compile:
(fragment of lindet-gen.scala):145:
error: value div is not a member of T
a.data(i) = a.data(i).div(b.data(i))
I was told in #scala that this worked for someone else, but that was on 2.8. I've tried to get 2.8-rc1 going, but it doesn't compile for me. Is there any way to get this to work in 2.7.7?
