Suppose I have a generic class and I need a 2D array of generic type T. If I try the following
class Matrix<T>(width: Int, height: Int) {
val data: Array<Array<T>> = Array(width, arrayOfNulls<T>(height))
}
the compiler will throw an error saying "Cannot use 'T' as reified type parameter. Use a class instead.".
Just because the syntax has moved on a bit, here's my take on it:
class Array2D<T> (val xSize: Int, val ySize: Int, val array: Array<Array<T>>) {
companion object {
inline operator fun <reified T> invoke() = Array2D(0, 0, Array(0, { emptyArray<T>() }))
inline operator fun <reified T> invoke(xWidth: Int, yWidth: Int) =
Array2D(xWidth, yWidth, Array(xWidth, { arrayOfNulls<T>(yWidth) }))
inline operator fun <reified T> invoke(xWidth: Int, yWidth: Int, operator: (Int, Int) -> (T)): Array2D<T> {
val array = Array(xWidth, {
val x = it
Array(yWidth, {operator(x, it)})})
return Array2D(xWidth, yWidth, array)
}
}
operator fun get(x: Int, y: Int): T {
return array[x][y]
}
operator fun set(x: Int, y: Int, t: T) {
array[x][y] = t
}
inline fun forEach(operation: (T) -> Unit) {
array.forEach { it.forEach { operation.invoke(it) } }
}
inline fun forEachIndexed(operation: (x: Int, y: Int, T) -> Unit) {
array.forEachIndexed { x, p -> p.forEachIndexed { y, t -> operation.invoke(x, y, t) } }
}
}
This also allows you to create 2d arrays in a similar manner to 1d arrays, e.g. something like
val array2D = Array2D<String>(5, 5) { x, y -> "$x $y" }
并使用索引操作符访问/设置内容:
val xy = array2D[1, 2]