Ilya Ryzhenkov
117 lines
4.3 KiB
Kotlin
117 lines
4.3 KiB
Kotlin
package iterators
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import kotlin.test.assertEquals
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import org.junit.Test as test
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import kotlin.test.fails
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import java.util.ArrayList
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fun fibonacci(): Stream<Int> {
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// fibonacci terms
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var index = 0; var a = 0; var b = 1
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return stream<Int> { when (index++) { 0 -> a; 1 -> b; else -> { val result = a + b; a = b; b = result; result } } }
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}
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class IteratorsTest {
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test fun filterAndTakeWhileExtractTheElementsWithinRange() {
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assertEquals(arrayListOf(144, 233, 377, 610, 987), fibonacci().filter { it > 100 }.takeWhile { it < 1000 }.toList())
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}
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test fun foldReducesTheFirstNElements() {
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val sum = { (a: Int, b: Int) -> a + b }
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assertEquals(arrayListOf(13, 21, 34, 55, 89).fold(0, sum), fibonacci().filter { it > 10 }.take(5).fold(0, sum))
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}
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test fun takeExtractsTheFirstNElements() {
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assertEquals(arrayListOf(0, 1, 1, 2, 3, 5, 8, 13, 21, 34), fibonacci().take(10).toList())
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}
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test fun mapAndTakeWhileExtractTheTransformedElements() {
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assertEquals(arrayListOf(0, 3, 3, 6, 9, 15), fibonacci().map { it * 3 }.takeWhile { (i: Int) -> i < 20 }.toList())
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}
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test fun mapIndexed() {
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assertEquals(arrayListOf(0, 1, 2, 6, 12), fibonacci().mapIndexed { index, value -> index * value }.takeWhile {(i: Int) -> i < 20 }.toList())
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}
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test fun joinConcatenatesTheFirstNElementsAboveAThreshold() {
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assertEquals("13, 21, 34, 55, 89, ...", fibonacci().filter { it > 10 }.joinToString(separator = ", ", limit = 5))
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}
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test fun plus() {
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val iter = arrayListOf("foo", "bar").stream()
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val iter2 = iter + "cheese"
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assertEquals(arrayListOf("foo", "bar", "cheese"), iter2.toList())
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// lets use a mutable variable
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var mi = streamOf("a", "b")
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mi += "c"
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assertEquals(arrayListOf("a", "b", "c"), mi.toList())
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}
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test fun plusCollection() {
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val a = arrayListOf("foo", "bar")
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val b = arrayListOf("cheese", "wine")
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val iter = a.stream() + b.stream()
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assertEquals(arrayListOf("foo", "bar", "cheese", "wine"), iter.toList())
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// lets use a mutable variable
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var ml = arrayListOf("a").stream()
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ml += a.stream()
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ml += "beer"
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ml += b
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ml += "z"
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assertEquals(arrayListOf("a", "foo", "bar", "beer", "cheese", "wine", "z"), ml.toList())
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}
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test fun requireNoNulls() {
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val iter = arrayListOf<String?>("foo", "bar").stream()
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val notNull = iter.requireNoNulls()
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assertEquals(arrayListOf("foo", "bar"), notNull.toList())
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val iterWithNulls = arrayListOf("foo", null, "bar").stream()
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val notNull2 = iterWithNulls.requireNoNulls()
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fails {
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// should throw an exception as we have a null
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notNull2.toList()
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}
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}
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test fun toStringJoinsNoMoreThanTheFirstTenElements() {
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assertEquals("0, 1, 1, 2, 3, 5, 8, 13, 21, 34, ...", fibonacci().joinToString(limit = 10))
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assertEquals("13, 21, 34, 55, 89, 144, 233, 377, 610, 987, ...", fibonacci().filter { it > 10 }.joinToString(limit = 10))
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assertEquals("144, 233, 377, 610, 987", fibonacci().filter { it > 100 }.takeWhile { it < 1000 }.joinToString())
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}
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test fun pairIterator() {
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val pairStr = (fibonacci() zip fibonacci().map { i -> i*2 }).joinToString(limit = 10)
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assertEquals("(0, 0), (1, 2), (1, 2), (2, 4), (3, 6), (5, 10), (8, 16), (13, 26), (21, 42), (34, 68), ...", pairStr)
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}
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test fun skippingIterator() {
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assertEquals("13, 21, 34, 55, 89, 144, 233, 377, 610, 987, ...", fibonacci().drop(7).joinToString(limit = 10))
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assertEquals("13, 21, 34, 55, 89, 144, 233, 377, 610, 987, ...", fibonacci().drop(3).drop(4).joinToString(limit = 10))
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}
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test fun iterationOverIterator() {
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val c = arrayListOf(0, 1, 2, 3, 4, 5)
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var s = ""
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for (i in c.iterator()) {
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s = s + i.toString()
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}
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assertEquals("012345", s)
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}
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private fun <T, C : MutableCollection<in T>> Iterator<T>.takeWhileTo(result: C, predicate: (T) -> Boolean): C {
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for (element in this) if (predicate(element)) result.add(element) else break
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return result
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}
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test fun iterableExtension() {
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val c = arrayListOf(0, 1, 2, 3, 4, 5)
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val d = ArrayList<Int>()
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c.iterator().takeWhileTo(d, {i -> i < 4 })
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assertEquals(4, d.size())
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}
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}
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