added an experiment of compositional map/filter style functions on nullables to mimick Scala's Option behaviour without any wrapper classes

2012-03-17 09:35:35 +00:00
parent d66077ea06
commit ed6ffe34fa
2 changed files with 202 additions and 18 deletions
@@ -0,0 +1,184 @@
+package kotlin.nullable
+
+import java.util.*
+import kotlin.util.getOrPut
+
+/** Returns true if the element is not null and matches the given predicate */
+inline fun <T> T?.any(predicate: (T)-> Boolean): Boolean {
+    return this != null && predicate(this)
+}
+
+/** Returns true if the element is not null and matches the given predicate */
+inline fun <T> T?.all(predicate: (T)-> Boolean): Boolean {
+    return this != null && predicate(this)
+}
+
+/** Returns the 1 if the element is not null else 0  */
+inline fun <T> T?.count(predicate: (T)-> Boolean): Int {
+    return if (this != null) 1 else 0
+}
+
+/** Returns the first item which matches the predicate if this element is not null else null */
+inline fun <T> T?.find(predicate: (T)-> Boolean): T? {
+    return if (this != null && predicate(this)) this else null
+}
+
+/** Returns a new List containing all elements in this collection which match the given predicate */
+inline fun <T> T?.filter(predicate: (T)-> Boolean): T? = find(predicate)
+
+/** Filters all elements in this collection which match the given predicate into the given result collection */
+inline fun <T, C: Collection<in T>> T?.filterTo(result: C, predicate: (T)-> Boolean): C {
+    if (this != null && predicate(this))
+        result.add(this)
+    return result
+}
+
+/** Returns a List containing all the non null elements in this collection */
+inline fun <T> T?.filterNotNull(): Collection<T> = filterNotNullTo(java.util.ArrayList<T>())
+
+/** Filters all the null elements in this collection winto the given result collection */
+inline fun <T, C: Collection<in T>> T?.filterNotNullTo(result: C): C {
+    if (this != null) {
+        result.add(this)
+    }
+    return result
+}
+
+/** Returns a new collection containing all elements in this collection which do not match the given predicate */
+inline fun <T> T?.filterNot(predicate: (T)-> Boolean): Collection<T> = filterNotTo(ArrayList<T>(), predicate)
+
+/** Returns a new collection containing all elements in this collection which do not match the given predicate */
+inline fun <T, C: Collection<in T>> T?.filterNotTo(result: C, predicate: (T)-> Boolean): C {
+    if (this != null && !predicate(this)) {
+        result.add(this)
+    }
+    return result
+}
+
+/**
+  * Returns the result of transforming each item in the collection to a one or more values which
+  * are concatenated together into a single collection
+  */
+inline fun <T, R> T?.flatMap(transform: (T)-> Collection<R>): Collection<R> {
+    return flatMapTo(ArrayList<R>(), transform)
+}
+
+/**
+  * Returns the result of transforming each item in the collection to a one or more values which
+  * are concatenated together into a single collection
+  */
+inline fun <T, R> T?.flatMapTo(result: Collection<R>, transform: (T)-> Collection<R>): Collection<R> {
+    if (this != null) {
+        val coll = transform(this)
+        if (coll != null) {
+            for (r in coll) {
+                result.add(r)
+            }
+        }
+    }
+    return result
+}
+
+/** Performs the given operation on each element inside the collection */
+inline fun <T> T?.forEach(operation: (element: T) -> Unit) {
+    if (this != null) {
+        operation(this)
+    }
+}
+
+/**
+ * Folds all the values from from left to right with the initial value to perform the operation on sequential pairs of values
+ *
+ * For example to sum together all numeric values in a collection of numbers it would be
+ * {code}val total = numbers.fold(0){(a, b) -> a + b}{code}
+ */
+inline fun <T> T?.fold(initial: T, operation: (it: T, it2: T) -> T): T {
+    return if (this != null) {
+        operation(initial, this)
+    } else {
+        initial
+    }
+}
+
+/**
+ * Folds all the values from right to left with the initial value to perform the operation on sequential pairs of values
+ */
+inline fun <T> T?.foldRight(initial: T, operation: (it: T, it2: T) -> T): T {
+    // maximum size is 1 so it makes no difference :)
+    return fold(initial, operation)
+}
+
+/**
+ * Iterates through the collection performing the transformation on each element and using the result
+ * as the key in a map to group elements by the result
+ */
+inline fun <T, K> T?.groupBy(result: Map<K, List<T>> = HashMap<K, List<T>>(), toKey: (T)-> K): Map<K, List<T>> {
+    if (this != null) {
+        val key = toKey(this)
+        val list = result.getOrPut(key){ ArrayList<T>() }
+        list.add(this)
+    }
+    return result
+}
+
+
+/** Creates a String from the nullable or item with the given prefix and postfix if supplied */
+inline fun <T> T?.join(separator: String, prefix: String = "", postfix: String = ""): String {
+    val buffer = StringBuilder(prefix)
+    var first = true
+    if (this != null) {
+        buffer.append(this)
+    }
+    buffer.append(postfix)
+    return buffer.toString().sure()
+}
+
+
+/** Returns the nullable result of transforming this with the given transformation function */
+inline fun <T, R> T?.map(transform : (T) -> R) : R? {
+    return if (this != null) {
+        transform(this)
+    } else {
+        null
+    }
+}
+
+/** Transforms each element of this collection with the given function then adds the results to the given collection */
+inline fun <T, R, C: Collection<in R>> T?.mapTo(result: C, transform : (T) -> R) : C {
+    if (this != null) {
+        result.add(transform(this))
+    }
+    return result
+}
+
+/** Returns itself since it can't be reversed as it can contain at most one item */
+inline fun <T> T?.reverse(): T? {
+    return this
+}
+
+/** Copies the collection into the given collection */
+inline fun <T, C: Collection<T>> T?.to(result: C): C {
+    if (this != null)
+        result.add(this)
+    return result
+}
+
+/** Converts the collection into a LinkedList */
+inline fun <T> T?.toLinkedList(): LinkedList<T> = this.to(LinkedList<T>())
+
+/**  Converts the collection into a List */
+inline fun <T> T?.toList(): List<T> = this.to(ArrayList<T>())
+
+/** Converts the collection into a Set */
+inline fun <T> T?.toSet(): Set<T> = this.to(HashSet<T>())
+
+/** Converts the collection into a SortedSet */
+inline fun <T> T?.toSortedSet(): SortedSet<T> = this.to(TreeSet<T>())
+/**
+  TODO figure out necessary variance/generics ninja stuff... :)
+inline fun <in T> T?.toSortedList(transform: fun(T) : java.lang.Comparable<*>) : List<T> {
+  val answer = this.toList()
+  answer.sort(transform)
+  return answer
+}
+*/