removed the create() methods; added linkedList<T>(varargs) helper method and made filter/flatMap/map all allow an optional argument for the kind of collection to filter/flatMap/map into. I've temporarily commented out Alex's implementation of Iterable.filter in Filters.kt as I was getting all kinds of compile error messages. Will discuss this on the list & how better to organise the functions into files

testlib/test/CollectionTest.kt

@@ -1,11 +1,11 @@
 namespace test.collections
 
-import std.test.*
-
 // TODO can we avoid importing all this stuff by default I wonder?
 // e.g. making println and the collection builder methods public by default?
+import std.*
 import std.io.*
 import std.util.*
+import std.test.*
 import java.util.*
 
 class CollectionTest() : TestSupport() {
@@ -39,6 +39,36 @@ class CollectionTest() : TestSupport() {
     assertEquals(arrayList("foo"), foo)
   }
 
+  fun testFilterIntoLinkedList() {
+    // TODO would be nice to avoid the <String>
+    val foo = data.filter(linkedList<String>()){it.startsWith("f")}
+
+    assert {
+      foo.all{it.startsWith("f")}
+    }
+    assertEquals(1, foo.size)
+    assertEquals(linkedList("foo"), foo)
+
+    assert {
+      foo is LinkedList<String>
+    }
+  }
+
+  fun testFilterIntoSortedSet() {
+    // TODO would be nice to avoid the <String>
+    val foo = data.filter(hashSet<String>()){it.startsWith("f")}
+
+    assert {
+      foo.all{it.startsWith("f")}
+    }
+    assertEquals(1, foo.size)
+    assertEquals(hashSet("foo"), foo)
+
+    assert {
+      foo is HashSet<String>
+    }
+  }
+
   fun testFind() {
     val x = data.find{it.startsWith("x")}
     assertNull(x)