Copy link from dart2js to own package.

pkg/compiler_util/lib/link.dart

+// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+part of dart2js.util;
+
+class Link<T> implements Iterable<T> {
+  T get head => throw new StateError("no elements");
+  Link<T> get tail => null;
+
+  const Link();
+
+  Link<T> prepend(T element) {
+    return new LinkEntry<T>(element, this);
+  }
+
+  Iterator<T> get iterator => new LinkIterator<T>(this);
+
+  void printOn(StringBuffer buffer, [separatedBy]) {}
+
+  List<T> toList({bool growable: true}) {
+    List<T> result;
+    if (!growable) {
+      result = new List<T>(slowLength());
+    } else {
+      result = new List<T>();
+      result.length = slowLength();
+    }
+    int i = 0;
+    for (Link<T> link = this; !link.isEmpty; link = link.tail) {
+      result[i++] = link.head;
+    }
+    return result;
+  }
+
+  /// Lazily maps over this linked list, returning an [Iterable].
+  Iterable map(dynamic fn(T item)) {
+    return new MappedLinkIterable<T, dynamic>(this, fn);
+  }
+
+  /// Invokes `fn` for every item in the linked list and returns the results
+  /// in a [List].
+  List mapToList(dynamic fn(T item), {bool growable: true}) {
+    List result;
+    if (!growable) {
+      result = new List(slowLength());
+    } else {
+      result = new List();
+      result.length = slowLength();
+    }
+    int i = 0;
+    for (Link<T> link = this; !link.isEmpty; link = link.tail) {
+      result[i++] = fn(link.head);
+    }
+    return result;
+  }
+
+  bool get isEmpty => true;
+  bool get isNotEmpty => false;
+
+  Link<T> reverse() => this;
+
+  Link<T> reversePrependAll(Link<T> from) {
+    if (from.isEmpty) return this;
+    return this.prepend(from.head).reversePrependAll(from.tail);
+  }
+
+  Link<T> skip(int n) {
+    if (n == 0) return this;
+    throw new RangeError('Index $n out of range');
+  }
+
+  void forEach(void f(T element)) {}
+
+  bool operator ==(other) {
+    if (other is! Link<T>) return false;
+    return other.isEmpty;
+  }
+
+  int get hashCode => throw new UnsupportedError('Link.hashCode');
+
+  String toString() => "[]";
+
+  get length {
+    throw new UnsupportedError('get:length');
+  }
+
+  int slowLength() => 0;
+
+  // TODO(ahe): Remove this method?
+  bool contains(T element) {
+    for (Link<T> link = this; !link.isEmpty; link = link.tail) {
+      if (link.head == element) return true;
+    }
+    return false;
+  }
+
+  // TODO(ahe): Remove this method?
+  T get single {
+    if (isEmpty) throw new StateError('No elements');
+    if (!tail.isEmpty) throw new StateError('More than one element');
+    return head;
+  }
+
+  // TODO(ahe): Remove this method?
+  T get first {
+    if (isEmpty) throw new StateError('No elements');
+    return head;
+  }
+
+  /// Returns true if f returns true for all elements of this list.
+  ///
+  /// Returns true for the empty list.
+  bool every(bool f(T)) {
+    for (Link<T> link = this; !link.isEmpty; link = link.tail) {
+      if (!f(link.head)) return false;
+    }
+    return true;
+  }
+
+  Link copyWithout(e) => this;
+
+  //
+  // Unsupported Iterable<T> methods.
+  //
+  bool any(bool f(T e)) => _unsupported('any');
+  T elementAt(int i) => _unsupported('elementAt');
+  Iterable expand(Iterable f(T e)) => _unsupported('expand');
+  T firstWhere(bool f(T e), {T orElse()}) => _unsupported('firstWhere');
+  fold(initialValue, combine(value, T element)) => _unsupported('fold');
+  T get last => _unsupported('get:last');
+  T lastWhere(bool f(T e), {T orElse()}) => _unsupported('lastWhere');
+  String join([separator = '']) => _unsupported('join');
+  T reduce(T combine(T a, T b)) => _unsupported('reduce');
+  T singleWhere(bool f(T e)) => _unsupported('singleWhere');
+  Iterable<T> skipWhile(bool f(T e)) => _unsupported('skipWhile');
+  Iterable<T> take(int n) => _unsupported('take');
+  Iterable<T> takeWhile(bool f(T e)) => _unsupported('takeWhile');
+  Set<T> toSet() => _unsupported('toSet');
+  Iterable<T> where(bool f(T e)) => _unsupported('where');
+
+  _unsupported(String method) => throw new UnsupportedError(method);
+}
+
+/// Builder object for creating linked lists using [Link] or fixed-length [List]
+/// objects.
+abstract class LinkBuilder<T> {
+  factory LinkBuilder() = LinkBuilderImplementation;
+
+  /// Prepends all elements added to the builder to [tail]. The resulting list
+  /// is returned and the builder is cleared.
+  Link<T> toLink([Link<T> tail = const Link()]);
+
+  /// Creates a new fixed length containing all added elements. The
+  /// resulting list is returned and the builder is cleared.
+  List<T> toList();
+
+  /// Adds the element [t] to the end of the list being built.
+  Link<T> addLast(T t);
+
+  /// Returns the first element in the list being built.
+  T get first;
+
+  /// Returns the number of elements in the list being built.
+  final int length;
+
+  /// Returns `true` if the list being built is empty.
+  final bool isEmpty;
+
+  /// Removes all added elements and resets the builder.
+  void clear();
+}