methods for iterators and filters

stdlib/ktSrc/Filter.kt

@@ -0,0 +1,62 @@
+namespace std
+
+import java.util.*
+import java.lang.Iterable
+
+/*
+Filters given iterator
+*/
+inline fun <T> java.util.Iterator<T>.filter(f: fun(T): Boolean) : java.util.Iterator<T> = FilterIterator<T>(this, f)
+
+/*
+Adds filtered elements in to given container
+*/
+inline fun <T,U : Collection<in T>> java.lang.Iterable<T>.filterTo(var container: U, filter: fun(T): Boolean) : U {
+   for(element in this) {
+      if(filter(element))
+        container.add(element)
+   }
+   return container
+}
+
+/*
+Create iterator filtering given java.lang.Iterable
+*/
+inline fun <T> java.lang.Iterable<T>.filter(f: fun(T): Boolean) : java.util.Iterator<T> = (iterator() as java.util.Iterator<T>).filter(f)
+
+private class FilterIterator<T>(val original: java.util.Iterator<T>, val filter: fun(T): Boolean) : java.util.Iterator<T> {
+    var state = 0
+    var nextElement: T? = null
+
+    override fun hasNext(): Boolean =
+        when(state) {
+                1 => true  // checked and next present
+                2 => false // checked and next not present
+                else => {
+                    while(original.hasNext()) {
+                        val candidate = original.next()
+                        if((filter)(candidate)) {
+                            nextElement = candidate
+                            state = 1
+                            true
+                        }
+                    }
+                    state = 2
+                    false
+                }
+        }
+
+    override fun next(): T =
+        if(state != 1)
+            throw java.util.NoSuchElementException()
+        else {
+            val res = nextElement as T
+            nextElement = null
+            state = 0
+            res
+        }
+
+    override fun remove() {
+        throw java.lang.UnsupportedOperationException()
+    }
+}

stdlib/ktSrc/Iterators.kt

@@ -0,0 +1,38 @@
+namespace std.util
+
+import java.util.*
+import java.util.Iterator
+
+/*
+Add iterated elements to given container
+*/
+fun <T,U: Collection<in T>> java.util.Iterator<T>.to(container: U) : U {
+    while(hasNext())
+        container.add(next())
+    return container
+}
+
+/*
+Add iterated elements to java.util.ArrayList
+*/
+inline fun <T> java.util.Iterator<T>.toArrayList() = to(ArrayList<T>())
+
+/*
+Add iterated elements to java.util.LinkedList
+*/
+inline fun <T> java.util.Iterator<T>.toLinkedList() = to(LinkedList<T>())
+
+/*
+Add iterated elements to java.util.HashSet
+*/
+inline fun <T> java.util.Iterator<T>.toHashSet() = to(HashSet<T>())
+
+/*
+Add iterated elements to java.util.LinkedHashSet
+*/
+inline fun <T> java.util.Iterator<T>.toLinkedHashSet() = to(LinkedHashSet<T>())
+
+/*
+Add iterated elements to java.util.TreeSet
+*/
+inline fun <T> java.util.Iterator<T>.toTreeSet() = to(TreeSet<T>())

stdlib/ktSrc/JavaUtil.kt

@@ -77,6 +77,7 @@ inline fun <T> java.lang.Iterable<T>.find(predicate: fun(T): Boolean) : T? {
 /** Returns a new collection containing all elements in this collection which match the given predicate */
 // TODO using: Collection<T> for the return type - I wonder if this exact type could be
 // deduced somewhat from the This.Type; e.g. returning Set on a Set, Array on Array etc
+/*
 inline fun <T> java.lang.Iterable<T>.filter(predicate: fun(T): Boolean) : Collection<T> {
   val result = this.create<T,T>()
   for (elem in this) {
@@ -85,6 +86,7 @@ inline fun <T> java.lang.Iterable<T>.filter(predicate: fun(T): Boolean) : Collec
   }
   return result
 }
+*/
 
 /**
   * Returns the result of transforming each item in the collection to a one or more values which