Deprecate .set .list and .map in favour of asList, asSet and asMap

lib/src/collection/extension/iterable_extension_mixin.dart

@@ -1213,7 +1213,8 @@ abstract class KtIterableExtensionsMixin<T>
       return true;
     }());
     final mutableList = toMutableList();
-    mutableList.list.sort(comparator);
+    // delegate to darts list implementation for sorting which is highly optimized
+    mutableList.asList().sort(comparator);
     return mutableList;
   }
 
@@ -1458,8 +1459,8 @@ class _MovingSubList<T> {
   _MovingSubList(this.list);
 
   KtList<T> list;
-  var _fromIndex = 0;
-  var _size = 0;
+  int _fromIndex = 0;
+  int _size = 0;
 
   void move(int fromIndex, int toIndex) {
     if (fromIndex < 0 || toIndex > list.size) {

lib/src/collection/extension/list_mutable_extension_mixin.dart

@@ -50,7 +50,8 @@ abstract class KtMutableListExtensionsMixin<T>
       if (comparator == null) throw ArgumentError("comparator can't be null");
       return true;
     }());
-    list.sort(comparator);
+    // delegate to darts list implementation for sorting which is highly optimized
+    asList().sort(comparator);
   }
 
   @override

lib/src/collection/extension/map_extensions_mixin.dart

@@ -3,6 +3,40 @@ import 'package:kt_dart/src/util/errors.dart';
 
 abstract class KtMapExtensionsMixin<K, V>
     implements KtMapExtension<K, V>, KtMap<K, V> {
+  @override
+  bool all(Function(K key, V value) predicate) {
+    assert(() {
+      if (predicate == null) throw ArgumentError("predicate can't be null");
+      return true;
+    }());
+    if (isEmpty()) {
+      return true;
+    }
+    for (KtMapEntry<K, V> entry in entries.iter) {
+      if (!predicate(entry.key, entry.value)) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  @override
+  bool any(Function(K key, V value) predicate) {
+    assert(() {
+      if (predicate == null) throw ArgumentError("predicate can't be null");
+      return true;
+    }());
+    if (isEmpty()) {
+      return false;
+    }
+    for (KtMapEntry<K, V> entry in entries.iter) {
+      if (predicate(entry.key, entry.value)) {
+        return true;
+      }
+    }
+    return false;
+  }
+
   @override
   KtMap<K, V> filter(bool Function(KtMapEntry<K, V> entry) predicate) {
     final filtered = filterTo(linkedMapFrom<K, V>(), predicate);
@@ -196,7 +230,7 @@ abstract class KtMapExtensionsMixin<K, V>
 
   @override
   KtMutableMap<K, V> toMutableMap() {
-    return mutableMapFrom(map);
+    return mutableMapFrom(asMap());
   }
 
   @override
@@ -225,40 +259,6 @@ abstract class KtMapExtensionsMixin<K, V>
     return true;
   }
 
-  @override
-  bool all(Function(K key, V value) predicate) {
-    assert(() {
-      if (predicate == null) throw ArgumentError("predicate can't be null");
-      return true;
-    }());
-    if (isEmpty()) {
-      return true;
-    }
-    for (KtMapEntry<K, V> entry in entries.iter) {
-      if (!predicate(entry.key, entry.value)) {
-        return false;
-      }
-    }
-    return true;
-  }
-
-  @override
-  bool any(Function(K key, V value) predicate) {
-    assert(() {
-      if (predicate == null) throw ArgumentError("predicate can't be null");
-      return true;
-    }());
-    if (isEmpty()) {
-      return false;
-    }
-    for (KtMapEntry<K, V> entry in entries.iter) {
-      if (predicate(entry.key, entry.value)) {
-        return true;
-      }
-    }
-    return false;
-  }
-
   @override
   String toString() {
     return entries.joinToString(

lib/src/collection/impl/dart_unmodifiable_set_view.dart

@@ -0,0 +1,84 @@
+import 'dart:collection';
+
+/// An unmodifiable set.
+///
+/// An UnmodifiableSetView contains a [Set] object and ensures
+/// that it does not change.
+/// Methods that would change the set,
+/// such as [add] and [remove], throw an [UnsupportedError].
+/// Permitted operations defer to the wrapped set.
+class UnmodifiableSetView<E> with IterableMixin<E> implements Set<E> {
+  UnmodifiableSetView(Set<E> set) : _set = set;
+
+  final Set<E> _set;
+
+  @override
+  Iterator<E> get iterator => _set.iterator;
+
+  @override
+  int get length => _set.length;
+
+  @override
+  Set<T> cast<T>() => _set.cast<T>();
+
+  @override
+  bool containsAll(Iterable<Object> other) => _set.containsAll(other);
+
+  @override
+  Set<E> difference(Set<Object> other) => _set.difference(other);
+
+  @override
+  Set<E> intersection(Set<Object> other) => _set.intersection(other);
+
+  @override
+  E lookup(Object object) => _set.lookup(object);
+
+  @override
+  Set<E> union(Set<E> other) => _set.union(other);
+
+  @override
+  Set<E> toSet() => _set.toSet();
+
+  static T _throw<T>() =>
+      throw UnsupportedError("Cannot modify an unmodifiable Set");
+
+  /// Throws an [UnsupportedError];
+  /// operations that change the set are disallowed.
+  @override
+  bool add(E value) => _throw();
+
+  /// Throws an [UnsupportedError];
+  /// operations that change the set are disallowed.
+  @override
+  void addAll(Iterable<E> elements) => _throw();
+
+  /// Throws an [UnsupportedError];
+  /// operations that change the set are disallowed.
+  @override
+  bool remove(Object value) => _throw();
+
+  /// Throws an [UnsupportedError];
+  /// operations that change the set are disallowed.
+  @override
+  void removeAll(Iterable elements) => _throw();
+
+  /// Throws an [UnsupportedError];
+  /// operations that change the set are disallowed.
+  @override
+  void retainAll(Iterable elements) => _throw();
+
+  /// Throws an [UnsupportedError];
+  /// operations that change the set are disallowed.
+  @override
+  void removeWhere(bool test(E element)) => _throw();
+
+  /// Throws an [UnsupportedError];
+  /// operations that change the set are disallowed.
+  @override
+  void retainWhere(bool test(E element)) => _throw();
+
+  /// Throws an [UnsupportedError];
+  /// operations that change the set are disallowed.
+  @override
+  void clear() => _throw();
+}

lib/src/collection/impl/iterator.dart

@@ -11,7 +11,7 @@ class InterOpKIterator<T> implements KtIterator<T> {
   final Iterator<T> iterator;
   T nextValue;
   T lastReturned;
-  var _hasNext = false;
+  bool _hasNext;
 
   @override
   bool hasNext() {

lib/src/collection/impl/list.dart

@@ -16,7 +16,7 @@ class DartList<T>
     implements KtList<T> {
   /// Create an immutable [KtList] by copying the incoming [iterable] into a [List]
   DartList([Iterable<T> iterable = const []])
-      : _list = List.from(iterable, growable: false),
+      : _list = List.unmodifiable(iterable),
         super();
 
   final List<T> _list;
@@ -28,6 +28,9 @@ class DartList<T>
   @override
   List<T> get list => _list;
 
+  @override
+  List<T> asList() => _list;
+
   @override
   bool contains(T element) => _list.contains(element);
 

lib/src/collection/impl/list_empty.dart

@@ -11,7 +11,10 @@ class EmptyList<T>
         KtListExtensionsMixin<T>
     implements KtList<T> {
   @override
-  List<T> get list => <T>[];
+  List<T> get list => List.unmodifiable([]);
+
+  @override
+  List<T> asList() => List.unmodifiable([]);
 
   @override
   bool contains(T element) => false;

lib/src/collection/impl/list_mutable.dart

@@ -34,6 +34,9 @@ class DartMutableList<T>
   @override
   List<T> get list => _list;
 
+  @override
+  List<T> asList() => _list;
+
   @override
   bool contains(T element) => _list.contains(element);
 

lib/src/collection/impl/map.dart

@@ -13,7 +13,10 @@ class DartMap<K, V> with KtMapExtensionsMixin<K, V> implements KtMap<K, V> {
   int _hashCode;
 
   @override
-  Map<K, V> get map => _map;
+  Iterable<MapEntry<K, V>> get iter => _map.entries;
+
+  @override
+  Map<K, V> asMap() => _map;
 
   @override
   bool containsKey(K key) => _map.containsKey(key);
@@ -70,9 +73,8 @@ class DartMap<K, V> with KtMapExtensionsMixin<K, V> implements KtMap<K, V> {
 class _Entry<K, V> extends KtMapEntry<K, V> {
   _Entry(this.key, this.value);
 
-  _Entry.from(MapEntry<K, V> entry)
-      : key = entry.key,
-        value = entry.value;
+  factory _Entry.from(MapEntry<K, V> entry) => _Entry(entry.key, entry.value);
+
   @override
   final K key;
 

lib/src/collection/impl/map_empty.dart

@@ -3,7 +3,10 @@ import 'package:kt_dart/src/collection/extension/map_extensions_mixin.dart';
 
 class EmptyMap<K, V> with KtMapExtensionsMixin<K, V> implements KtMap<K, V> {
   @override
-  Map<K, V> get map => {};
+  Iterable<MapEntry<K, V>> get iter => List.unmodifiable([]);
+
+  @override
+  Map<K, V> asMap() => Map.unmodifiable({});
 
   @override
   V operator [](K key) => null;

lib/src/collection/impl/map_mutable.dart

@@ -22,7 +22,10 @@ class DartMutableMap<K, V>
   final Map<K, V> _map;
 
   @override
-  Map<K, V> get map => _map;
+  Iterable<MapEntry<K, V>> get iter => _map.entries;
+
+  @override
+  Map<K, V> asMap() => _map;
 
   @override
   bool containsKey(K key) => _map.containsKey(key);
@@ -117,9 +120,8 @@ class DartMutableMap<K, V>
 class _MutableEntry<K, V> implements KtMutableMapEntry<K, V> {
   _MutableEntry(this._key, this._value);
 
-  _MutableEntry.from(MapEntry<K, V> entry)
-      : _key = entry.key,
-        _value = entry.value;
+  factory _MutableEntry.from(MapEntry<K, V> entry) =>
+      _MutableEntry(entry.key, entry.value);
 
   K _key;
   V _value;

lib/src/collection/impl/set.dart

@@ -1,13 +1,14 @@
 import 'package:kt_dart/collection.dart';
 import 'package:kt_dart/src/collection/extension/collection_extension_mixin.dart';
 import 'package:kt_dart/src/collection/extension/iterable_extension_mixin.dart';
+import 'package:kt_dart/src/collection/impl/dart_unmodifiable_set_view.dart';
 import 'package:kt_dart/src/util/hash.dart';
 
 class DartSet<T>
     with KtIterableExtensionsMixin<T>, KtCollectionExtensionMixin<T>
     implements KtSet<T> {
   DartSet([Iterable<T> iterable = const []])
-      : _set = Set.from(iterable),
+      : _set = UnmodifiableSetView(Set.from(iterable)),
         super();
 
   final Set<T> _set;
@@ -23,6 +24,9 @@ class DartSet<T>
     return Set.of(_set);
   }
 
+  @override
+  Set<T> asSet() => _set;
+
   @override
   bool contains(T element) => _set.contains(element);
 
@@ -75,7 +79,7 @@ class _DartToKIterator<T> extends KtIterator<T> {
   final Iterator<T> iterator;
   T nextValue;
   T lastReturned;
-  var _hasNext = false;
+  bool _hasNext;
 
   @override
   bool hasNext() {

lib/src/collection/impl/set_empty.dart

@@ -1,3 +1,4 @@
+import 'package:collection/collection.dart';
 import 'package:kt_dart/collection.dart';
 import 'package:kt_dart/src/collection/extension/collection_extension_mixin.dart';
 import 'package:kt_dart/src/collection/extension/iterable_extension_mixin.dart';
@@ -7,7 +8,10 @@ class EmptySet<T>
     with KtIterableExtensionsMixin<T>, KtCollectionExtensionMixin<T>
     implements KtSet<T> {
   @override
-  Set<T> get set => Set();
+  Set<T> get set => UnmodifiableSetView(Set());
+
+  @override
+  Set<T> asSet() => UnmodifiableSetView(Set());
 
   @override
   bool contains(T element) => false;

lib/src/collection/impl/set_mutable.dart

@@ -29,6 +29,9 @@ class DartMutableSet<T>
   @override
   Set<T> get set => _set;
 
+  @override
+  Set<T> asSet() => _set;
+
   @override
   bool contains(T element) => _set.contains(element);
 
@@ -127,7 +130,7 @@ class _MutableSetIterator<T> extends KtMutableIterator<T> {
   final Iterator<T> _iterator;
   T nextValue;
   T lastReturned;
-  var _hasNext = false;
+  bool _hasNext;
 
   @override
   bool hasNext() {