Update charted to 0.4.8 and roll

packages/quiver/lib/src/core/optional.dart

 // Copyright 2013 Google Inc. All Rights Reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
 part of quiver.core;
 
-/**
- * A value that might be absent.
- *
- * Use Optional as an alternative to allowing fields, parameters or return
- * values to be null. It signals that a value is not required and provides
- * convenience methods for dealing with the absent case.
- */
-class Optional<T> {
+/// A value that might be absent.
+///
+/// Use Optional as an alternative to allowing fields, parameters or return
+/// values to be null. It signals that a value is not required and provides
+/// convenience methods for dealing with the absent case.
+class Optional<T> extends IterableBase<T> {
   final T _value;
 
-  /**
-   * Constructs an empty Optional.
-   */
+  /// Constructs an empty Optional.
   const Optional.absent() : _value = null;
 
-  /**
-   * Constructs an Optional of the given [value].
-   *
-   * Throws [ArgumentError] if [value] is null.
-   */
+  /// Constructs an Optional of the given [value].
+  ///
+  /// Throws [ArgumentError] if [value] is null.
   Optional.of(T value) : this._value = value {
     if (this._value == null) throw new ArgumentError('Must not be null.');
   }
 
-  /**
-   * Constructs an Optional of the given [value].
-   *
-   * If [value] is null, returns [absent()].
-   */
+  /// Constructs an Optional of the given [value].
+  ///
+  /// If [value] is null, returns [absent()].
   const Optional.fromNullable(T value) : this._value = value;
 
-  /**
-   * Whether the Optional contains a value.
-   */
+  /// Whether the Optional contains a value.
   bool get isPresent => _value != null;
 
-  /**
-   * Gets the Optional value.
-   *
-   * Throws [StateError] if [value] is null.
-   */
+  /// Gets the Optional value.
+  ///
+  /// Throws [StateError] if [value] is null.
   T get value {
     if (this._value == null) {
       throw new StateError('value called on absent Optional.');
     }
     return _value;
   }
 
-  /**
-   * Executes a function if the Optional value is present.
-   */
+  /// Executes a function if the Optional value is present.
   void ifPresent(void ifPresent(T value)) {
     if (isPresent) {
       ifPresent(_value);
     }
   }
 
-  /**
-   * Execution a function if the Optional value is absent.
-   */
+  /// Execution a function if the Optional value is absent.
   void ifAbsent(void ifAbsent()) {
     if (!isPresent) {
       ifAbsent();
     }
   }
 
-  /**
-   * Gets the Optional value with a default.
-   *
-   * The default is returned if the Optional is [absent()].
-   *
-   * Throws [ArgumentError] if [defaultValue] is null.
-   */
+  /// Gets the Optional value with a default.
+  ///
+  /// The default is returned if the Optional is [absent()].
+  ///
+  /// Throws [ArgumentError] if [defaultValue] is null.
   T or(T defaultValue) {
     if (defaultValue == null) {
       throw new ArgumentError('defaultValue must not be null.');
     }
     return _value == null ? defaultValue : _value;
   }
 
-  /**
-   * Gets the Optional value, or [null] if there is none.
-   */
+  /// Gets the Optional value, or [null] if there is none.
   T get orNull => _value;
 
-  /**
-   * Transforms the Optional value.
-   *
-   * If the Optional is [absent()], returns [absent()] without applying the transformer.
-   *
-   * The transformer must not return [null]. If it does, an [ArgumentError] is thrown.
-   */
-  Optional transform(dynamic transformer(T value)) {
+  /// Transforms the Optional value.
+  ///
+  /// If the Optional is [absent()], returns [absent()] without applying the transformer.
+  ///
+  /// The transformer must not return [null]. If it does, an [ArgumentError] is thrown.
+  Optional<S> transform<S>(S transformer(T value)) {
     return _value == null
         ? new Optional.absent()
         : new Optional.of(transformer(_value));
   }
 
-  /**
-   * Delegates to the underlying [value] hashCode.
-   */
+  @override
+  Iterator<T> get iterator =>
+      isPresent ? <T>[_value].iterator : new Iterable<T>.empty().iterator;
+
+  /// Delegates to the underlying [value] hashCode.
   int get hashCode => _value.hashCode;
 
-  /**
-   * Delegates to the underlying [value] operator==.
-   */
+  /// Delegates to the underlying [value] operator==.
   bool operator ==(o) => o is Optional && o._value == _value;
 
   String toString() {
     return _value == null
         ? 'Optional { absent }'
         : 'Optional { value: ${_value} }';
   }
 }