initial psike of #KT-39 on collections (iterators required too), though hit #KT-1710

libraries/stdlib/src/kotlin/JLangIterables.kt

@@ -177,22 +177,25 @@ public inline fun <T> java.lang.Iterable<T>.reverse() : List<T> {
 }
 
 /** Copies all elements into the given collection */
-public inline fun <T, C: Collection<T>> java.lang.Iterable<T>.to(result: C) : C {
+public inline fun <in T, C: Collection<in T>> java.lang.Iterable<T>.to(result: C) : C {
     for (element in this) result.add(element)
     return result
 }
 
-/** Copies all elements into a [[LinkedList]] */
-public inline fun <T> java.lang.Iterable<T>.toLinkedList() : LinkedList<T> = to(LinkedList<T>())
+/** Copies all elements into a [[LinkedList]] if its not already a [[LinkedList]]  */
+public inline fun <in T> java.lang.Iterable<T>.toLinkedList() : LinkedList<T> = if (this is LinkedList<T>) this else to(LinkedList<T>())
 
-/** Copies all elements into a [[List]] */
-public inline fun <T> java.lang.Iterable<T>.toList() : List<T> = to(ArrayList<T>())
+/** Copies all elements into a [[List]] if its not already a [[List]] */
+public inline fun <in T> java.lang.Iterable<T>.toList() : List<T> = if (this is List<T>) this else to(ArrayList<T>())
 
-/** Copies all elements into a [[Set]] */
-public inline fun <T> java.lang.Iterable<T>.toSet() : Set<T> = to(HashSet<T>())
+/** Copies all elements into a [[List]] if it is not already a [[Collection]] */
+public inline fun <in T> java.lang.Iterable<T>.toCollection() : Collection<T> = if (this is Collection<T>) this else to(ArrayList<T>())
 
-/** Copies all elements into a [[SortedSet]] */
-public inline fun <T> java.lang.Iterable<T>.toSortedSet() : SortedSet<T> = to(TreeSet<T>())
+/** Copies all elements into a [[Set]] if its not already a [[Set]] */
+public inline fun <in T> java.lang.Iterable<T>.toSet() : Set<T> = if (this is Set<T>) this else to(HashSet<T>())
+
+/** Copies all elements into a [[SortedSet]] if its not already a [[SortedSet]] */
+public inline fun <in T> java.lang.Iterable<T>.toSortedSet() : SortedSet<T> = if (this is SortedSet<T>) this else to(TreeSet<T>())
 
 /**
   TODO figure out necessary variance/generics ninja stuff... :)

libraries/stdlib/src/kotlin/JUtil.kt

@@ -39,12 +39,58 @@ public inline fun <T> java.util.Collection<T>.toArray() : Array<T> {
   return answer as Array<T>
 }
 
-/** TODO these functions don't work when they generate the Array<T> versions when they are in JavaIterables */
+/** Returns true if the collection is not empty */
+public inline fun <T> java.util.Collection<T>.notEmpty() : Boolean = !this.isEmpty()
+
+/** Returns the Collection if its not null otherwise it returns the empty list */
+public inline fun <T> java.util.Collection<T>?.orEmpty() : Collection<T>
+    = if (this != null) this else Collections.EMPTY_LIST as Collection<T>
+
+
+/** TODO these functions don't work when they generate the Array<T> versions when they are in JLIterables */
 public inline fun <in T: java.lang.Comparable<T>> java.lang.Iterable<T>.toSortedList() : List<T> = toList().sort()
 
 public inline fun <in T: java.lang.Comparable<T>> java.lang.Iterable<T>.toSortedList(comparator: java.util.Comparator<T>) : List<T> = toList().sort(comparator)
 
 
+/**
+ * Creates a new [[List]] with the element added at the end
+ *
+ * @includeFunctionBody ../../test/CollectionTest.kt plus
+ */
+public inline fun <in T> java.util.Collection<T>.plus(element: T): List<in T> {
+    val list = to(ArrayList<T>())
+    list.add(element)
+    return list
+}
+
+/**
+ * Adds the element to this collection
+ *
+ * @includeFunctionBody ../../test/CollectionTest.kt plusAssign
+ */
+public inline fun <in T, C: java.util.Collection<in T>> C.plusAssign(element: T): C {
+    add(element)
+    return this
+}
+
+/**
+ * Creates a new [[List]] with the element added at the end
+ */
+/*
+public inline fun <in T> java.util.Collection<T>.plus(elements: java.lang.Iterable<T>): List<T> = toList().plusAssign(elements)
+*/
+
+/**
+ * Adds all the elements to this collection
+ */
+/*
+public inline fun <in T, C: Collection<in T>> C.plusAssign(elements: java.lang.Iterable<T>): C {
+    addAll(elements.toCollection())
+    return this
+}
+*/
+
 
 // List APIs
 
@@ -98,12 +144,3 @@ val <T> List<T>.tail : T?
 
 val <T> List<T>.last : T?
     get() = this.tail
-
-
-/** Returns true if the collection is not empty */
-public inline fun <T> java.util.Collection<T>.notEmpty() : Boolean = !this.isEmpty()
-
-/** Returns the Collection if its not null otherwise it returns the empty list */
-public inline fun <T> java.util.Collection<T>?.orEmpty() : Collection<T>
-    = if (this != null) this else Collections.EMPTY_LIST as Collection<T>
-