loop over BigInteger values using foreach in Kotlin - kotlin

Question

I am trying to loop over BigInteger values in Kotlin using the following code snippet. But it's telling For-loop range must have an 'iterator()' method. How can I loop over the BigInteger values in Kotlin?
private fun pow(base: BigInteger, power: BigInteger): String {
for(i in BigInteger.ZERO..power){ //Giving error
}
}

Answer 1

You can extend BigInteger to allow this
In particular we need to:
introduce rangeTo function to BigInteger (to allow using .. operator)
add iterator function to the range returned by rangeTo operator
The rangeTo function
Here I'm defining an extension function for BigInteger
operator fun BigInteger.rangeTo(other: BigInteger) =
BigIntegerRange(this, other)
BigIntegerRange:
class BigIntegerRange(
override val start: BigInteger,
override val endInclusive: BigInteger
) : ClosedRange<BigInteger>, Iterable<BigInteger> {
override operator fun iterator(): Iterator<BigInteger> =
BigIntegerRangeIterator(this)
}
BigIntegerRangeIterator:
class BigIntegerRangeIterator(
private val range: ClosedRange<BigInteger>
) : Iterator<BigInteger> {
private var current = range.start
override fun hasNext(): Boolean =
current <= range.endInclusive
override fun next(): BigInteger {
if (!hasNext()) {
throw NoSuchElementException()
}
return current++
}
}
Now this code:
fun main() {
for (i in BigInteger.ZERO..BigInteger.TEN) {
println(i)
}
}
Compiles and prints:
0
1
2
3
4
5
6
7
8
9
10
Do not forget to import the rangeTo function
See also:
Ranges
Control Flow. For Loops