From 30a627b018b814c7f382e6d7ea7abcf5cfbf8a61 Mon Sep 17 00:00:00 2001
From: David Morgan <davidmorgan@google.com>
Date: Sun, 11 Sep 2016 14:11:38 +0200
Subject: [PATCH] Generate builder if none is written by hand. toString appends
 commas. Improve examples and tests. Fix double null checking.

---
 CHANGELOG.md                                  |   7 +
 built_value/pubspec.yaml                      |   2 +-
 .../lib/src/source_class.dart                 |  71 +++++---
 .../lib/src/source_class.g.dart               |  45 ++----
 .../lib/src/source_field.dart                 |  77 +++++++--
 .../lib/src/source_field.g.dart               |  32 ++--
 built_value_generator/pubspec.yaml            |   6 +-
 .../test/built_value_generator_test.dart      |  10 --
 example/lib/collections.dart                  |  36 +++++
 example/lib/collections.g.dart                | 139 ++++++++++++++++
 example/lib/compound_value.dart               |  29 +---
 example/lib/compound_value.g.dart             |  39 +++--
 example/lib/simple_value.dart                 |  25 +++
 example/lib/simple_value.g.dart               |  60 +++++++
 example/lib/validated_value.dart              |  25 +++
 example/lib/validated_value.g.dart            |  62 +++++++
 example/lib/value.dart                        |  67 --------
 example/lib/value.g.dart                      |  90 -----------
 example/lib/value_with_code.dart              |  32 ++++
 example/lib/value_with_code.g.dart            |  61 +++++++
 example/lib/value_with_defaults.dart          |  42 +++++
 example/lib/value_with_defaults.g.dart        |  58 +++++++
 example/pubspec.yaml                          |  10 +-
 example/test/collections_test.dart            |  74 +++++++++
 example/test/compound_value_test.dart         |  20 ++-
 example/test/simple_value_test.dart           |  95 +++++++++++
 example/test/validated_value_test.dart        |  18 +++
 example/test/value_test.dart                  | 152 ------------------
 example/test/value_with_code_test.dart        |  26 +++
 example/test/value_with_defaults_test.dart    |  14 ++
 30 files changed, 978 insertions(+), 446 deletions(-)
 create mode 100644 example/lib/collections.dart
 create mode 100644 example/lib/collections.g.dart
 create mode 100644 example/lib/simple_value.dart
 create mode 100644 example/lib/simple_value.g.dart
 create mode 100644 example/lib/validated_value.dart
 create mode 100644 example/lib/validated_value.g.dart
 delete mode 100644 example/lib/value.dart
 delete mode 100644 example/lib/value.g.dart
 create mode 100644 example/lib/value_with_code.dart
 create mode 100644 example/lib/value_with_code.g.dart
 create mode 100644 example/lib/value_with_defaults.dart
 create mode 100644 example/lib/value_with_defaults.g.dart
 create mode 100644 example/test/collections_test.dart
 create mode 100644 example/test/simple_value_test.dart
 create mode 100644 example/test/validated_value_test.dart
 delete mode 100644 example/test/value_test.dart
 create mode 100644 example/test/value_with_code_test.dart
 create mode 100644 example/test/value_with_defaults_test.dart

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6b5770a8..535d272f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,12 @@
 # Changelog
 
+## 0.1.3
+
+- Generate builder if it's not written by hand.
+- Make toString append commas for improved clarity.
+- Improve examples and tests.
+- Fix double null checking.
+
 ## 0.1.2
 
 - Refactor generator to split into logical classes.
diff --git a/built_value/pubspec.yaml b/built_value/pubspec.yaml
index 5df1265a..0b7aebc8 100644
--- a/built_value/pubspec.yaml
+++ b/built_value/pubspec.yaml
@@ -1,5 +1,5 @@
 name: built_value
-version: 0.1.2
+version: 0.1.3
 description: >
   Value types with builders. This library is the runtime dependency.
 authors:
diff --git a/built_value_generator/lib/src/source_class.dart b/built_value_generator/lib/src/source_class.dart
index 9761404e..18e9a144 100644
--- a/built_value_generator/lib/src/source_class.dart
+++ b/built_value_generator/lib/src/source_class.dart
@@ -50,12 +50,12 @@ abstract class SourceClass implements Built<SourceClass, SourceClassBuilder> {
           .map((constructor) => constructor.computeNode().toSource()))
       ..valueClassFactories.replace(classElement.constructors
           .where((constructor) => constructor.isFactory)
-          .map((factory) => factory.computeNode().toSource()));
+          .map((factory) => factory.computeNode().toSource()))
+      ..fields.replace(
+          SourceField.fromClassElements(classElement, builderClassElement));
 
     if (hasBuilder) {
       result
-        ..fields.replace(
-            SourceField.fromClassElements(classElement, builderClassElement))
         ..builderClassIsAbstract = builderClassElement.isAbstract
         ..builderClassConstructors.replace(builderClassElement.constructors
             .where((constructor) =>
@@ -127,10 +127,7 @@ abstract class SourceClass implements Built<SourceClass, SourceClassBuilder> {
 
   Iterable<String> _checkBuilderClass() {
     final result = <String>[];
-
-    if (!hasBuilder) {
-      return <String>['Add abstract class: ${name}Builder'];
-    }
+    if (!hasBuilder) return result;
 
     if (!builderClassIsAbstract) {
       result.add('Make builder class abstract.');
@@ -154,6 +151,7 @@ abstract class SourceClass implements Built<SourceClass, SourceClassBuilder> {
   }
 
   Iterable<String> _checkFieldList() {
+    if (!hasBuilder) return <String>[];
     return fields.any((field) => !field.builderFieldExists)
         ? [
             'Make builder have exactly these fields: ' +
@@ -172,6 +170,7 @@ abstract class SourceClass implements Built<SourceClass, SourceClassBuilder> {
     for (final field in fields) {
       result.writeln('final ${field.type} ${field.name};');
     }
+    result.writeln();
 
     if (fields.isEmpty) {
       result.write('_\$$name._() : super._() {');
@@ -184,14 +183,25 @@ abstract class SourceClass implements Built<SourceClass, SourceClassBuilder> {
       result.writeln("if (${field.name} == null) "
           "throw new ArgumentError('null ${field.name}');");
     }
-    result.write('}');
+    result.writeln('}');
+    result.writeln();
 
     result.writeln('factory _\$$name([updates(${name}Builder b)]) '
         '=> (new ${name}Builder()..update(updates)).build();');
+    result.writeln();
+
     result.writeln('$name rebuild(updates(${name}Builder b)) '
         '=> (toBuilder()..update(updates)).build();');
-    result.writeln('_\$${name}Builder toBuilder() '
-        '=> new _\$${name}Builder()..replace(this);');
+    result.writeln();
+
+    if (hasBuilder) {
+      result.writeln('_\$${name}Builder toBuilder() '
+          '=> new _\$${name}Builder()..replace(this);');
+    } else {
+      result.writeln('${name}Builder toBuilder() '
+          '=> new ${name}Builder()..replace(this);');
+    }
+    result.writeln();
 
     result.writeln('bool operator==(other) {');
     result.writeln('  if (other is! $name) return false;');
@@ -205,6 +215,7 @@ abstract class SourceClass implements Built<SourceClass, SourceClassBuilder> {
       result.writeln(';');
     }
     result.writeln('}');
+    result.writeln();
 
     result.writeln('int get hashCode {');
     if (fields.length == 0) {
@@ -215,6 +226,7 @@ abstract class SourceClass implements Built<SourceClass, SourceClassBuilder> {
       result.writeln(']);');
     }
     result.writeln('}');
+    result.writeln();
 
     result.writeln('String toString() {');
     if (fields.length == 0) {
@@ -222,35 +234,54 @@ abstract class SourceClass implements Built<SourceClass, SourceClassBuilder> {
     } else {
       result.writeln("return '$name {'");
       result.writeln(fields
-          .map((field) => "'${field.name}=\${${field.name}.toString()}\\n'")
+          .map((field) => "'${field.name}=\${${field.name}.toString()},\\n'")
           .join(''));
       result.writeln("'}'");
       result.writeln(';');
     }
     result.writeln('}');
+    result.writeln();
 
     result.writeln('}');
 
-    result.writeln('class _\$${name}Builder extends ${name}Builder {');
-    result.writeln();
-    result.writeln('_\$${name}Builder() : super._();');
+    if (hasBuilder) {
+      result.writeln('class _\$${name}Builder extends ${name}Builder {');
+      result.writeln('_\$${name}Builder() : super._();');
+    } else {
+      result.writeln(
+          'class ${name}Builder implements Builder<$name, ${name}Builder>{');
+      result.writeln('${name}Builder();');
+    }
+
+    if (!hasBuilder) {
+      for (final field in fields) {
+        // Nested builders are initialized to an empty builder, unless the
+        // field is nullable.
+        if (field.isNestedBuilder && !field.isNullable) {
+          result.writeln('${field.typeInBuilder} ${field.name} = new ${field.typeInBuilder}();');
+        } else {
+          result.writeln('${field.typeInBuilder} ${field.name};');
+        }
+      }
+      result.writeln();
+    }
 
     result.writeln('void replace(${name} other) {');
     result.writeln((fields.map((field) {
+      final superOrThis = hasBuilder ? 'super' : 'this';
       return field.isNestedBuilder
-          ? 'super.${field.name} = other.${field.name}?.toBuilder();'
-          : 'super.${field.name} = other.${field.name};';
+          ? '$superOrThis.${field.name} = other.${field.name}?.toBuilder();'
+          : '$superOrThis.${field.name} = other.${field.name};';
     }))
         .join('\n'));
     result.writeln('}');
+    result.writeln();
 
     result.writeln('void update(updates(${name}Builder b)) {'
         ' if (updates != null) updates(this); }');
+    result.writeln();
+
     result.writeln('$name build() {');
-    for (final field in fields.where((field) => !field.isNullable)) {
-      result.writeln("if (${field.name} == null) "
-          "throw new ArgumentError('null ${field.name}');");
-    }
     result.writeln('return new _\$$name._(');
     result.write(fields.map((field) {
       return field.isNestedBuilder
diff --git a/built_value_generator/lib/src/source_class.g.dart b/built_value_generator/lib/src/source_class.g.dart
index 2e355e8b..33924259 100644
--- a/built_value_generator/lib/src/source_class.g.dart
+++ b/built_value_generator/lib/src/source_class.g.dart
@@ -19,6 +19,7 @@ class _$SourceClass extends SourceClass {
   final bool builderClassIsAbstract;
   final BuiltList<String> builderClassConstructors;
   final BuiltList<String> builderClassFactories;
+
   _$SourceClass._(
       {this.name,
       this.hasBuilder,
@@ -51,11 +52,15 @@ class _$SourceClass extends SourceClass {
     if (builderClassFactories == null)
       throw new ArgumentError('null builderClassFactories');
   }
+
   factory _$SourceClass([updates(SourceClassBuilder b)]) =>
       (new SourceClassBuilder()..update(updates)).build();
+
   SourceClass rebuild(updates(SourceClassBuilder b)) =>
       (toBuilder()..update(updates)).build();
+
   _$SourceClassBuilder toBuilder() => new _$SourceClassBuilder()..replace(this);
+
   bool operator ==(other) {
     if (other is! SourceClass) return false;
     return name == other.name &&
@@ -89,17 +94,17 @@ class _$SourceClass extends SourceClass {
 
   String toString() {
     return 'SourceClass {'
-        'name=${name.toString()}\n'
-        'hasBuilder=${hasBuilder.toString()}\n'
-        'fields=${fields.toString()}\n'
-        'partStatement=${partStatement.toString()}\n'
-        'hasPartStatement=${hasPartStatement.toString()}\n'
-        'valueClassIsAbstract=${valueClassIsAbstract.toString()}\n'
-        'valueClassConstructors=${valueClassConstructors.toString()}\n'
-        'valueClassFactories=${valueClassFactories.toString()}\n'
-        'builderClassIsAbstract=${builderClassIsAbstract.toString()}\n'
-        'builderClassConstructors=${builderClassConstructors.toString()}\n'
-        'builderClassFactories=${builderClassFactories.toString()}\n'
+        'name=${name.toString()},\n'
+        'hasBuilder=${hasBuilder.toString()},\n'
+        'fields=${fields.toString()},\n'
+        'partStatement=${partStatement.toString()},\n'
+        'hasPartStatement=${hasPartStatement.toString()},\n'
+        'valueClassIsAbstract=${valueClassIsAbstract.toString()},\n'
+        'valueClassConstructors=${valueClassConstructors.toString()},\n'
+        'valueClassFactories=${valueClassFactories.toString()},\n'
+        'builderClassIsAbstract=${builderClassIsAbstract.toString()},\n'
+        'builderClassConstructors=${builderClassConstructors.toString()},\n'
+        'builderClassFactories=${builderClassFactories.toString()},\n'
         '}';
   }
 }
@@ -126,24 +131,6 @@ class _$SourceClassBuilder extends SourceClassBuilder {
   }
 
   SourceClass build() {
-    if (name == null) throw new ArgumentError('null name');
-    if (hasBuilder == null) throw new ArgumentError('null hasBuilder');
-    if (fields == null) throw new ArgumentError('null fields');
-    if (partStatement == null) throw new ArgumentError('null partStatement');
-    if (hasPartStatement == null)
-      throw new ArgumentError('null hasPartStatement');
-    if (valueClassIsAbstract == null)
-      throw new ArgumentError('null valueClassIsAbstract');
-    if (valueClassConstructors == null)
-      throw new ArgumentError('null valueClassConstructors');
-    if (valueClassFactories == null)
-      throw new ArgumentError('null valueClassFactories');
-    if (builderClassIsAbstract == null)
-      throw new ArgumentError('null builderClassIsAbstract');
-    if (builderClassConstructors == null)
-      throw new ArgumentError('null builderClassConstructors');
-    if (builderClassFactories == null)
-      throw new ArgumentError('null builderClassFactories');
     return new _$SourceClass._(
         name: name,
         hasBuilder: hasBuilder,
diff --git a/built_value_generator/lib/src/source_field.dart b/built_value_generator/lib/src/source_field.dart
index fe10cc14..c945b6d8 100644
--- a/built_value_generator/lib/src/source_field.dart
+++ b/built_value_generator/lib/src/source_field.dart
@@ -5,11 +5,20 @@
 library built_value_generator.source_field;
 
 import 'package:analyzer/dart/element/element.dart';
+import 'package:analyzer/dart/element/type.dart';
 import 'package:built_collection/built_collection.dart';
 import 'package:built_value/built_value.dart';
 
 part 'source_field.g.dart';
 
+BuiltSet<String> _builtCollectionNames = new BuiltSet<String>([
+  'BuiltList',
+  'BuiltListMultimap',
+  'BuiltMap',
+  'BuiltSet',
+  'BuiltSetMultimap',
+]);
+
 abstract class SourceField implements Built<SourceField, SourceFieldBuilder> {
   String get name;
   String get type;
@@ -17,7 +26,6 @@ abstract class SourceField implements Built<SourceField, SourceFieldBuilder> {
   bool get isNullable;
   bool get builderFieldExists;
   bool get builderFieldIsNormalField;
-  @nullable
   String get typeInBuilder;
   bool get isNestedBuilder;
 
@@ -26,22 +34,35 @@ abstract class SourceField implements Built<SourceField, SourceFieldBuilder> {
 
   factory SourceField.fromFieldElements(
       FieldElement fieldElement, FieldElement builderFieldElement) {
-    return new SourceField((b) => b
+    final result = new SourceFieldBuilder();
+    final builderFieldExists = builderFieldElement != null;
+    final type = fieldElement.getter.returnType.displayName;
+    result
       ..name = fieldElement.displayName
-      ..type = fieldElement.getter.returnType.displayName
-      ..typeInBuilder = builderFieldElement?.getter?.returnType?.displayName
+      ..type = type
       ..isGetter =
           fieldElement.getter != null && !fieldElement.getter.isSynthetic
       ..isNullable = fieldElement.getter.metadata.any(
-          (metadata) => metadata.constantValue.toStringValue() == 'nullable')
-      ..builderFieldExists = builderFieldElement != null
-      ..builderFieldIsNormalField = builderFieldElement != null &&
-          builderFieldElement.getter != null &&
-          !builderFieldElement.getter.isAbstract &&
-          builderFieldElement.getter.isSynthetic
-      ..isNestedBuilder = builderFieldElement?.getter?.returnType?.displayName
-              ?.contains('Builder') ??
-          false);
+          (metadata) => metadata.constantValue.toStringValue() == 'nullable');
+
+    if (builderFieldExists) {
+      result
+        ..builderFieldExists = true
+        ..builderFieldIsNormalField = builderFieldElement.getter != null &&
+            !builderFieldElement.getter.isAbstract &&
+            builderFieldElement.getter.isSynthetic
+        ..typeInBuilder = builderFieldElement.getter?.returnType?.displayName
+        ..isNestedBuilder = builderFieldElement.getter?.returnType?.displayName
+                ?.contains('Builder') ??
+            false;
+    } else {
+      result
+        ..builderFieldExists = false
+        ..builderFieldIsNormalField = true
+        ..typeInBuilder = _toBuilderType(fieldElement.getter.returnType)
+        ..isNestedBuilder = _needsNestedBuilder(fieldElement.getter.returnType);
+    }
+    return result.build();
   }
 
   static BuiltList<SourceField> fromClassElements(
@@ -52,7 +73,7 @@ abstract class SourceField implements Built<SourceField, SourceFieldBuilder> {
       if (!field.isStatic &&
           field.getter != null &&
           (field.getter.isAbstract || field.getter.isSynthetic)) {
-        final builderField = builderClassElement.getField(field.name);
+        final builderField = builderClassElement?.getField(field.name);
         result.add(new SourceField.fromFieldElements(field, builderField));
       }
     }
@@ -60,6 +81,34 @@ abstract class SourceField implements Built<SourceField, SourceFieldBuilder> {
     return result.build();
   }
 
+  static bool _needsNestedBuilder(DartType type) {
+    return _isBuiltValue(type) || _isBuiltCollection(type);
+  }
+
+  static bool _isBuiltValue(DartType type) {
+    if (type.element is! ClassElement) return false;
+    return (type.element as ClassElement)
+        .allSupertypes
+        .any((interfaceType) => interfaceType.name == 'Built');
+  }
+
+  static bool _isBuiltCollection(DartType type) {
+    return _builtCollectionNames
+        .any((name) => type.displayName.startsWith('${name}<'));
+  }
+
+  static String _toBuilderType(DartType type) {
+    if (_isBuiltCollection(type)) {
+      return type.displayName
+          .replaceFirst('Built', '')
+          .replaceFirst('<', 'Builder<');
+    } else if (_isBuiltValue(type)) {
+      return '${type.displayName}Builder';
+    } else {
+      return type.displayName;
+    }
+  }
+
   Iterable<String> computeErrors() {
     final result = <String>[];
 
diff --git a/built_value_generator/lib/src/source_field.g.dart b/built_value_generator/lib/src/source_field.g.dart
index 7f3ef206..e506526e 100644
--- a/built_value_generator/lib/src/source_field.g.dart
+++ b/built_value_generator/lib/src/source_field.g.dart
@@ -16,6 +16,7 @@ class _$SourceField extends SourceField {
   final bool builderFieldIsNormalField;
   final String typeInBuilder;
   final bool isNestedBuilder;
+
   _$SourceField._(
       {this.name,
       this.type,
@@ -34,14 +35,19 @@ class _$SourceField extends SourceField {
       throw new ArgumentError('null builderFieldExists');
     if (builderFieldIsNormalField == null)
       throw new ArgumentError('null builderFieldIsNormalField');
+    if (typeInBuilder == null) throw new ArgumentError('null typeInBuilder');
     if (isNestedBuilder == null)
       throw new ArgumentError('null isNestedBuilder');
   }
+
   factory _$SourceField([updates(SourceFieldBuilder b)]) =>
       (new SourceFieldBuilder()..update(updates)).build();
+
   SourceField rebuild(updates(SourceFieldBuilder b)) =>
       (toBuilder()..update(updates)).build();
+
   _$SourceFieldBuilder toBuilder() => new _$SourceFieldBuilder()..replace(this);
+
   bool operator ==(other) {
     if (other is! SourceField) return false;
     return name == other.name &&
@@ -69,14 +75,14 @@ class _$SourceField extends SourceField {
 
   String toString() {
     return 'SourceField {'
-        'name=${name.toString()}\n'
-        'type=${type.toString()}\n'
-        'isGetter=${isGetter.toString()}\n'
-        'isNullable=${isNullable.toString()}\n'
-        'builderFieldExists=${builderFieldExists.toString()}\n'
-        'builderFieldIsNormalField=${builderFieldIsNormalField.toString()}\n'
-        'typeInBuilder=${typeInBuilder.toString()}\n'
-        'isNestedBuilder=${isNestedBuilder.toString()}\n'
+        'name=${name.toString()},\n'
+        'type=${type.toString()},\n'
+        'isGetter=${isGetter.toString()},\n'
+        'isNullable=${isNullable.toString()},\n'
+        'builderFieldExists=${builderFieldExists.toString()},\n'
+        'builderFieldIsNormalField=${builderFieldIsNormalField.toString()},\n'
+        'typeInBuilder=${typeInBuilder.toString()},\n'
+        'isNestedBuilder=${isNestedBuilder.toString()},\n'
         '}';
   }
 }
@@ -99,16 +105,6 @@ class _$SourceFieldBuilder extends SourceFieldBuilder {
   }
 
   SourceField build() {
-    if (name == null) throw new ArgumentError('null name');
-    if (type == null) throw new ArgumentError('null type');
-    if (isGetter == null) throw new ArgumentError('null isGetter');
-    if (isNullable == null) throw new ArgumentError('null isNullable');
-    if (builderFieldExists == null)
-      throw new ArgumentError('null builderFieldExists');
-    if (builderFieldIsNormalField == null)
-      throw new ArgumentError('null builderFieldIsNormalField');
-    if (isNestedBuilder == null)
-      throw new ArgumentError('null isNestedBuilder');
     return new _$SourceField._(
         name: name,
         type: type,
diff --git a/built_value_generator/pubspec.yaml b/built_value_generator/pubspec.yaml
index fbb90715..9f48e4de 100644
--- a/built_value_generator/pubspec.yaml
+++ b/built_value_generator/pubspec.yaml
@@ -1,5 +1,5 @@
 name: built_value_generator
-version: 0.1.2
+version: 0.1.3
 description: >
   Value types with builders. This library is the dev dependency.
 authors:
@@ -13,7 +13,9 @@ dependencies:
   analyzer: '>=0.27.1 <0.28.0'
   build: '^0.3.0'
   built_collection: '^1.0.0'
-  built_value: '^0.1.2'
+#  built_value: '^0.1.2'
+  built_value:
+    path: ../built_value
   source_gen: '>=0.5.0+03 <0.6.0'
   quiver: '>=0.21.0 <0.22.0'
 
diff --git a/built_value_generator/test/built_value_generator_test.dart b/built_value_generator/test/built_value_generator_test.dart
index 796eda7a..d2473fa2 100644
--- a/built_value_generator/test/built_value_generator_test.dart
+++ b/built_value_generator/test/built_value_generator_test.dart
@@ -100,16 +100,6 @@ abstract class ValueBuilder extends Builder<Value, ValueBuilder> {
               "factory Value([updates(ValueBuilder b)]) = _\$Value;"));
     });
 
-    test('suggests to add builder class', () async {
-      expect(await generate('''library value;
-import 'package:built_value/built_value.dart';
-part 'value.g.dart';
-abstract class Value extends Built<Value, ValueBuilder> {
-  Value._();
-  factory Value([updates(ValueBuilder b)]) = _\$Value;
-}'''), contains("1. Add abstract class: ValueBuilder"));
-    });
-
     test('suggests to make builder class abstract', () async {
       expect(await generate('''library value;
 import 'package:built_value/built_value.dart';
diff --git a/example/lib/collections.dart b/example/lib/collections.dart
new file mode 100644
index 00000000..e51a729a
--- /dev/null
+++ b/example/lib/collections.dart
@@ -0,0 +1,36 @@
+// Copyright (c) 2016, Google Inc. 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.
+
+library collections;
+
+import 'package:built_collection/built_collection.dart';
+import 'package:built_value/built_value.dart';
+
+part 'collections.g.dart';
+
+/// Example of how to use built_value.
+///
+/// Classes can contain collections; these must be from built_collection. In
+/// the builder, the builder corresponding to the collection is provided.
+abstract class Collections implements Built<Collections, CollectionsBuilder> {
+  BuiltList<int> get list;
+  BuiltSet<String> get set;
+  BuiltMap<String, int> get map;
+  BuiltListMultimap<int, bool> get listMultimap;
+  BuiltSetMultimap<String, bool> get setMultimap;
+
+  @nullable
+  BuiltList<int> get nullableList;
+  @nullable
+  BuiltSet<String> get nullableSet;
+  @nullable
+  BuiltMap<String, int> get nullableMap;
+  @nullable
+  BuiltListMultimap<int, bool> get nullableListMultimap;
+  @nullable
+  BuiltSetMultimap<String, bool> get nullableSetMultimap;
+
+  Collections._();
+  factory Collections([updates(CollectionsBuilder b)]) = _$Collections;
+}
diff --git a/example/lib/collections.g.dart b/example/lib/collections.g.dart
new file mode 100644
index 00000000..13fc12e6
--- /dev/null
+++ b/example/lib/collections.g.dart
@@ -0,0 +1,139 @@
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+part of collections;
+
+// **************************************************************************
+// Generator: BuiltValueGenerator
+// Target: abstract class Collections
+// **************************************************************************
+
+class _$Collections extends Collections {
+  final BuiltList<int> list;
+  final BuiltSet<String> set;
+  final BuiltMap<String, int> map;
+  final BuiltListMultimap<int, bool> listMultimap;
+  final BuiltSetMultimap<String, bool> setMultimap;
+  final BuiltList<int> nullableList;
+  final BuiltSet<String> nullableSet;
+  final BuiltMap<String, int> nullableMap;
+  final BuiltListMultimap<int, bool> nullableListMultimap;
+  final BuiltSetMultimap<String, bool> nullableSetMultimap;
+
+  _$Collections._(
+      {this.list,
+      this.set,
+      this.map,
+      this.listMultimap,
+      this.setMultimap,
+      this.nullableList,
+      this.nullableSet,
+      this.nullableMap,
+      this.nullableListMultimap,
+      this.nullableSetMultimap})
+      : super._() {
+    if (list == null) throw new ArgumentError('null list');
+    if (set == null) throw new ArgumentError('null set');
+    if (map == null) throw new ArgumentError('null map');
+    if (listMultimap == null) throw new ArgumentError('null listMultimap');
+    if (setMultimap == null) throw new ArgumentError('null setMultimap');
+  }
+
+  factory _$Collections([updates(CollectionsBuilder b)]) =>
+      (new CollectionsBuilder()..update(updates)).build();
+
+  Collections rebuild(updates(CollectionsBuilder b)) =>
+      (toBuilder()..update(updates)).build();
+
+  CollectionsBuilder toBuilder() => new CollectionsBuilder()..replace(this);
+
+  bool operator ==(other) {
+    if (other is! Collections) return false;
+    return list == other.list &&
+        set == other.set &&
+        map == other.map &&
+        listMultimap == other.listMultimap &&
+        setMultimap == other.setMultimap &&
+        nullableList == other.nullableList &&
+        nullableSet == other.nullableSet &&
+        nullableMap == other.nullableMap &&
+        nullableListMultimap == other.nullableListMultimap &&
+        nullableSetMultimap == other.nullableSetMultimap;
+  }
+
+  int get hashCode {
+    return hashObjects([
+      list,
+      set,
+      map,
+      listMultimap,
+      setMultimap,
+      nullableList,
+      nullableSet,
+      nullableMap,
+      nullableListMultimap,
+      nullableSetMultimap
+    ]);
+  }
+
+  String toString() {
+    return 'Collections {'
+        'list=${list.toString()},\n'
+        'set=${set.toString()},\n'
+        'map=${map.toString()},\n'
+        'listMultimap=${listMultimap.toString()},\n'
+        'setMultimap=${setMultimap.toString()},\n'
+        'nullableList=${nullableList.toString()},\n'
+        'nullableSet=${nullableSet.toString()},\n'
+        'nullableMap=${nullableMap.toString()},\n'
+        'nullableListMultimap=${nullableListMultimap.toString()},\n'
+        'nullableSetMultimap=${nullableSetMultimap.toString()},\n'
+        '}';
+  }
+}
+
+class CollectionsBuilder implements Builder<Collections, CollectionsBuilder> {
+  CollectionsBuilder();
+  ListBuilder<int> list = new ListBuilder<int>();
+  SetBuilder<String> set = new SetBuilder<String>();
+  MapBuilder<String, int> map = new MapBuilder<String, int>();
+  ListMultimapBuilder<int, bool> listMultimap =
+      new ListMultimapBuilder<int, bool>();
+  SetMultimapBuilder<String, bool> setMultimap =
+      new SetMultimapBuilder<String, bool>();
+  ListBuilder<int> nullableList;
+  SetBuilder<String> nullableSet;
+  MapBuilder<String, int> nullableMap;
+  ListMultimapBuilder<int, bool> nullableListMultimap;
+  SetMultimapBuilder<String, bool> nullableSetMultimap;
+
+  void replace(Collections other) {
+    this.list = other.list?.toBuilder();
+    this.set = other.set?.toBuilder();
+    this.map = other.map?.toBuilder();
+    this.listMultimap = other.listMultimap?.toBuilder();
+    this.setMultimap = other.setMultimap?.toBuilder();
+    this.nullableList = other.nullableList?.toBuilder();
+    this.nullableSet = other.nullableSet?.toBuilder();
+    this.nullableMap = other.nullableMap?.toBuilder();
+    this.nullableListMultimap = other.nullableListMultimap?.toBuilder();
+    this.nullableSetMultimap = other.nullableSetMultimap?.toBuilder();
+  }
+
+  void update(updates(CollectionsBuilder b)) {
+    if (updates != null) updates(this);
+  }
+
+  Collections build() {
+    return new _$Collections._(
+        list: list?.build(),
+        set: set?.build(),
+        map: map?.build(),
+        listMultimap: listMultimap?.build(),
+        setMultimap: setMultimap?.build(),
+        nullableList: nullableList?.build(),
+        nullableSet: nullableSet?.build(),
+        nullableMap: nullableMap?.build(),
+        nullableListMultimap: nullableListMultimap?.build(),
+        nullableSetMultimap: nullableSetMultimap?.build());
+  }
+}
diff --git a/example/lib/compound_value.dart b/example/lib/compound_value.dart
index 1b566edc..f535aebb 100644
--- a/example/lib/compound_value.dart
+++ b/example/lib/compound_value.dart
@@ -6,36 +6,21 @@ library compound_value;
 
 import 'package:built_value/built_value.dart';
 
-import 'value.dart';
+import 'package:example/validated_value.dart';
+import 'simple_value.dart';
 
 part 'compound_value.g.dart';
 
 /// Example of how to use built_value.
 ///
-/// The value class must implement [Built]. It must be abstract, and have
-/// fields declared as abstract getters. Finally, it must have a particular
-/// constructor and factory, as shown here.
+/// Other built_value classes can be used as fields. In the builder they are
+/// represented as nested builders.
 abstract class CompoundValue
     implements Built<CompoundValue, CompoundValueBuilder> {
-  Value get value;
+  SimpleValue get simpleValue;
+  @nullable
+  ValidatedValue get validatedValue;
 
   CompoundValue._();
   factory CompoundValue([updates(CompoundValueBuilder b)]) = _$CompoundValue;
 }
-
-/// The builder class must implement [Builder]. It must be abstract, and have
-/// fields declared as normal public fields. Finally, it must have a particular
-/// constructor and factory, as shown here.
-///
-/// Defaults can be specified by assigning them to fields here.
-///
-/// Validation can be done by overriding the [build] method.
-abstract class CompoundValueBuilder
-    implements Builder<CompoundValue, CompoundValueBuilder> {
-  ValueBuilder value = new ValueBuilder()
-    ..anInt = 0
-    ..aString = '1';
-
-  CompoundValueBuilder._();
-  factory CompoundValueBuilder() = _$CompoundValueBuilder;
-}
diff --git a/example/lib/compound_value.g.dart b/example/lib/compound_value.g.dart
index f488662f..499bee48 100644
--- a/example/lib/compound_value.g.dart
+++ b/example/lib/compound_value.g.dart
@@ -8,36 +8,48 @@ part of compound_value;
 // **************************************************************************
 
 class _$CompoundValue extends CompoundValue {
-  final Value value;
-  _$CompoundValue._({this.value}) : super._() {
-    if (value == null) throw new ArgumentError('null value');
+  final SimpleValue simpleValue;
+  final ValidatedValue validatedValue;
+
+  _$CompoundValue._({this.simpleValue, this.validatedValue}) : super._() {
+    if (simpleValue == null) throw new ArgumentError('null simpleValue');
   }
+
   factory _$CompoundValue([updates(CompoundValueBuilder b)]) =>
       (new CompoundValueBuilder()..update(updates)).build();
+
   CompoundValue rebuild(updates(CompoundValueBuilder b)) =>
       (toBuilder()..update(updates)).build();
-  _$CompoundValueBuilder toBuilder() =>
-      new _$CompoundValueBuilder()..replace(this);
+
+  CompoundValueBuilder toBuilder() => new CompoundValueBuilder()..replace(this);
+
   bool operator ==(other) {
     if (other is! CompoundValue) return false;
-    return value == other.value;
+    return simpleValue == other.simpleValue &&
+        validatedValue == other.validatedValue;
   }
 
   int get hashCode {
-    return hashObjects([value]);
+    return hashObjects([simpleValue, validatedValue]);
   }
 
   String toString() {
     return 'CompoundValue {'
-        'value=${value.toString()}\n'
+        'simpleValue=${simpleValue.toString()},\n'
+        'validatedValue=${validatedValue.toString()},\n'
         '}';
   }
 }
 
-class _$CompoundValueBuilder extends CompoundValueBuilder {
-  _$CompoundValueBuilder() : super._();
+class CompoundValueBuilder
+    implements Builder<CompoundValue, CompoundValueBuilder> {
+  CompoundValueBuilder();
+  SimpleValueBuilder simpleValue = new SimpleValueBuilder();
+  ValidatedValueBuilder validatedValue;
+
   void replace(CompoundValue other) {
-    super.value = other.value?.toBuilder();
+    this.simpleValue = other.simpleValue?.toBuilder();
+    this.validatedValue = other.validatedValue?.toBuilder();
   }
 
   void update(updates(CompoundValueBuilder b)) {
@@ -45,7 +57,8 @@ class _$CompoundValueBuilder extends CompoundValueBuilder {
   }
 
   CompoundValue build() {
-    if (value == null) throw new ArgumentError('null value');
-    return new _$CompoundValue._(value: value?.build());
+    return new _$CompoundValue._(
+        simpleValue: simpleValue?.build(),
+        validatedValue: validatedValue?.build());
   }
 }
diff --git a/example/lib/simple_value.dart b/example/lib/simple_value.dart
new file mode 100644
index 00000000..101174b7
--- /dev/null
+++ b/example/lib/simple_value.dart
@@ -0,0 +1,25 @@
+// Copyright (c) 2016, Google Inc. 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.
+
+library simple_value;
+
+import 'package:built_value/built_value.dart';
+
+part 'simple_value.g.dart';
+
+/// Example of how to use built_value.
+///
+/// The value class must implement [Built]. It must be abstract, and have
+/// fields declared as abstract getters. Finally, it must have a particular
+/// constructor and factory, as shown here.
+abstract class SimpleValue implements Built<SimpleValue, SimpleValueBuilder> {
+  int get anInt;
+
+  // Only fields marked @nullable can hold null.
+  @nullable
+  String get aString;
+
+  SimpleValue._();
+  factory SimpleValue([updates(SimpleValueBuilder b)]) = _$SimpleValue;
+}
diff --git a/example/lib/simple_value.g.dart b/example/lib/simple_value.g.dart
new file mode 100644
index 00000000..9b2506ae
--- /dev/null
+++ b/example/lib/simple_value.g.dart
@@ -0,0 +1,60 @@
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+part of simple_value;
+
+// **************************************************************************
+// Generator: BuiltValueGenerator
+// Target: abstract class SimpleValue
+// **************************************************************************
+
+class _$SimpleValue extends SimpleValue {
+  final int anInt;
+  final String aString;
+
+  _$SimpleValue._({this.anInt, this.aString}) : super._() {
+    if (anInt == null) throw new ArgumentError('null anInt');
+  }
+
+  factory _$SimpleValue([updates(SimpleValueBuilder b)]) =>
+      (new SimpleValueBuilder()..update(updates)).build();
+
+  SimpleValue rebuild(updates(SimpleValueBuilder b)) =>
+      (toBuilder()..update(updates)).build();
+
+  SimpleValueBuilder toBuilder() => new SimpleValueBuilder()..replace(this);
+
+  bool operator ==(other) {
+    if (other is! SimpleValue) return false;
+    return anInt == other.anInt && aString == other.aString;
+  }
+
+  int get hashCode {
+    return hashObjects([anInt, aString]);
+  }
+
+  String toString() {
+    return 'SimpleValue {'
+        'anInt=${anInt.toString()},\n'
+        'aString=${aString.toString()},\n'
+        '}';
+  }
+}
+
+class SimpleValueBuilder implements Builder<SimpleValue, SimpleValueBuilder> {
+  SimpleValueBuilder();
+  int anInt;
+  String aString;
+
+  void replace(SimpleValue other) {
+    this.anInt = other.anInt;
+    this.aString = other.aString;
+  }
+
+  void update(updates(SimpleValueBuilder b)) {
+    if (updates != null) updates(this);
+  }
+
+  SimpleValue build() {
+    return new _$SimpleValue._(anInt: anInt, aString: aString);
+  }
+}
diff --git a/example/lib/validated_value.dart b/example/lib/validated_value.dart
new file mode 100644
index 00000000..5c806be3
--- /dev/null
+++ b/example/lib/validated_value.dart
@@ -0,0 +1,25 @@
+// Copyright (c) 2016, Google Inc. Please see the AUTHORS file for details.
+// All rights reserved. Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+library validated_value;
+
+import 'package:built_value/built_value.dart';
+
+part 'validated_value.g.dart';
+
+/// Example of how to use built_value.
+///
+/// Validation can be done in the constructor.
+abstract class ValidatedValue
+    implements Built<ValidatedValue, ValidatedValueBuilder> {
+  int get anInt;
+  @nullable
+  String get aString;
+
+  ValidatedValue._() {
+    if (anInt == 7) throw 'anInt may not be 7';
+  }
+
+  factory ValidatedValue([updates(ValidatedValueBuilder b)]) = _$ValidatedValue;
+}
diff --git a/example/lib/validated_value.g.dart b/example/lib/validated_value.g.dart
new file mode 100644
index 00000000..370ca5f1
--- /dev/null
+++ b/example/lib/validated_value.g.dart
@@ -0,0 +1,62 @@
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+part of validated_value;
+
+// **************************************************************************
+// Generator: BuiltValueGenerator
+// Target: abstract class ValidatedValue
+// **************************************************************************
+
+class _$ValidatedValue extends ValidatedValue {
+  final int anInt;
+  final String aString;
+
+  _$ValidatedValue._({this.anInt, this.aString}) : super._() {
+    if (anInt == null) throw new ArgumentError('null anInt');
+  }
+
+  factory _$ValidatedValue([updates(ValidatedValueBuilder b)]) =>
+      (new ValidatedValueBuilder()..update(updates)).build();
+
+  ValidatedValue rebuild(updates(ValidatedValueBuilder b)) =>
+      (toBuilder()..update(updates)).build();
+
+  ValidatedValueBuilder toBuilder() =>
+      new ValidatedValueBuilder()..replace(this);
+
+  bool operator ==(other) {
+    if (other is! ValidatedValue) return false;
+    return anInt == other.anInt && aString == other.aString;
+  }
+
+  int get hashCode {
+    return hashObjects([anInt, aString]);
+  }
+
+  String toString() {
+    return 'ValidatedValue {'
+        'anInt=${anInt.toString()},\n'
+        'aString=${aString.toString()},\n'
+        '}';
+  }
+}
+
+class ValidatedValueBuilder
+    implements Builder<ValidatedValue, ValidatedValueBuilder> {
+  ValidatedValueBuilder();
+  int anInt;
+  String aString;
+
+  void replace(ValidatedValue other) {
+    this.anInt = other.anInt;
+    this.aString = other.aString;
+  }
+
+  void update(updates(ValidatedValueBuilder b)) {
+    if (updates != null) updates(this);
+  }
+
+  ValidatedValue build() {
+    return new _$ValidatedValue._(anInt: anInt, aString: aString);
+  }
+}
diff --git a/example/lib/value.dart b/example/lib/value.dart
deleted file mode 100644
index e00615aa..00000000
--- a/example/lib/value.dart
+++ /dev/null
@@ -1,67 +0,0 @@
-// Copyright (c) 2015, Google Inc. 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.
-
-library value;
-
-import 'package:built_collection/built_collection.dart';
-import 'package:built_value/built_value.dart';
-
-part 'value.g.dart';
-
-/// Example of how to use built_value.
-///
-/// The value class must implement [Built]. It must be abstract, and have
-/// fields declared as abstract getters. Finally, it must have a particular
-/// constructor and factory, as shown here.
-///
-/// Custom validation can be done in the constructor.
-abstract class Value implements Built<Value, ValueBuilder> {
-  static final int youCanHaveStaticFields = 3;
-
-  int get anInt;
-  String get aString;
-  @nullable
-  Object get anObject;
-  int get aDefaultInt;
-  BuiltList<int> get listOfInt;
-  @nullable
-  BuiltSet<String> get setOfString;
-
-  int get youCanWriteDerivedGetters => anInt + aDefaultInt;
-
-  Value._() {
-    // All fields are initialized before the constructor runs. So, custom
-    // validation can be done here.
-    if (anInt == 7) throw 'anInt may not be 7';
-  }
-  factory Value([updates(ValueBuilder b)]) = _$Value;
-
-  factory Value.fromCustomFactory() => new Value((b) => b
-    ..anInt = 1
-    ..aString = 'two');
-}
-
-/// The builder class must implement [Builder]. It must be abstract, and have
-/// fields declared as normal public fields. Finally, it must have a particular
-/// constructor and factory, as shown here.
-///
-/// Defaults can be specified by assigning them to fields here.
-abstract class ValueBuilder implements Builder<Value, ValueBuilder> {
-  int anInt;
-  String aString;
-  @nullable
-  Object anObject;
-  int aDefaultInt = 7;
-  ListBuilder<int> listOfInt = new ListBuilder<int>();
-  @nullable
-  SetBuilder<String> setOfString;
-
-  ValueBuilder._();
-  factory ValueBuilder() = _$ValueBuilder;
-
-  set youCanWriteExtraSetters(int value) {
-    anInt = value;
-    aDefaultInt = value;
-  }
-}
diff --git a/example/lib/value.g.dart b/example/lib/value.g.dart
deleted file mode 100644
index 7fe5f27d..00000000
--- a/example/lib/value.g.dart
+++ /dev/null
@@ -1,90 +0,0 @@
-// GENERATED CODE - DO NOT MODIFY BY HAND
-
-part of value;
-
-// **************************************************************************
-// Generator: BuiltValueGenerator
-// Target: abstract class Value
-// **************************************************************************
-
-class _$Value extends Value {
-  final int anInt;
-  final String aString;
-  final Object anObject;
-  final int aDefaultInt;
-  final BuiltList<int> listOfInt;
-  final BuiltSet<String> setOfString;
-  _$Value._(
-      {this.anInt,
-      this.aString,
-      this.anObject,
-      this.aDefaultInt,
-      this.listOfInt,
-      this.setOfString})
-      : super._() {
-    if (anInt == null) throw new ArgumentError('null anInt');
-    if (aString == null) throw new ArgumentError('null aString');
-    if (aDefaultInt == null) throw new ArgumentError('null aDefaultInt');
-    if (listOfInt == null) throw new ArgumentError('null listOfInt');
-  }
-  factory _$Value([updates(ValueBuilder b)]) =>
-      (new ValueBuilder()..update(updates)).build();
-  Value rebuild(updates(ValueBuilder b)) =>
-      (toBuilder()..update(updates)).build();
-  _$ValueBuilder toBuilder() => new _$ValueBuilder()..replace(this);
-  bool operator ==(other) {
-    if (other is! Value) return false;
-    return anInt == other.anInt &&
-        aString == other.aString &&
-        anObject == other.anObject &&
-        aDefaultInt == other.aDefaultInt &&
-        listOfInt == other.listOfInt &&
-        setOfString == other.setOfString;
-  }
-
-  int get hashCode {
-    return hashObjects(
-        [anInt, aString, anObject, aDefaultInt, listOfInt, setOfString]);
-  }
-
-  String toString() {
-    return 'Value {'
-        'anInt=${anInt.toString()}\n'
-        'aString=${aString.toString()}\n'
-        'anObject=${anObject.toString()}\n'
-        'aDefaultInt=${aDefaultInt.toString()}\n'
-        'listOfInt=${listOfInt.toString()}\n'
-        'setOfString=${setOfString.toString()}\n'
-        '}';
-  }
-}
-
-class _$ValueBuilder extends ValueBuilder {
-  _$ValueBuilder() : super._();
-  void replace(Value other) {
-    super.anInt = other.anInt;
-    super.aString = other.aString;
-    super.anObject = other.anObject;
-    super.aDefaultInt = other.aDefaultInt;
-    super.listOfInt = other.listOfInt?.toBuilder();
-    super.setOfString = other.setOfString?.toBuilder();
-  }
-
-  void update(updates(ValueBuilder b)) {
-    if (updates != null) updates(this);
-  }
-
-  Value build() {
-    if (anInt == null) throw new ArgumentError('null anInt');
-    if (aString == null) throw new ArgumentError('null aString');
-    if (aDefaultInt == null) throw new ArgumentError('null aDefaultInt');
-    if (listOfInt == null) throw new ArgumentError('null listOfInt');
-    return new _$Value._(
-        anInt: anInt,
-        aString: aString,
-        anObject: anObject,
-        aDefaultInt: aDefaultInt,
-        listOfInt: listOfInt?.build(),
-        setOfString: setOfString?.build());
-  }
-}
diff --git a/example/lib/value_with_code.dart b/example/lib/value_with_code.dart
new file mode 100644
index 00000000..04413676
--- /dev/null
+++ b/example/lib/value_with_code.dart
@@ -0,0 +1,32 @@
+// Copyright (c) 2016, Google Inc. 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.
+
+library value_with_code;
+
+import 'package:built_value/built_value.dart';
+
+part 'value_with_code.g.dart';
+
+/// Example of how to use built_value.
+///
+/// You can add static fields and methods, implement interfaces, add additonal
+/// factory constructor, and generally use the class as a normal class.
+abstract class ValueWithCode
+    implements Built<ValueWithCode, ValueWithCodeBuilder> {
+  static final int youCanHaveStaticFields = 3;
+
+  int get anInt;
+  @nullable
+  String get aString;
+
+  String get youCanWriteDerivedGetters => anInt.toString() + aString;
+
+  ValueWithCode._();
+  factory ValueWithCode([updates(ValueWithCodeBuilder b)]) = _$ValueWithCode;
+
+  factory ValueWithCode.fromCustomFactory(int anInt) =>
+      new ValueWithCode((b) => b
+        ..anInt = anInt
+        ..aString = 'two');
+}
diff --git a/example/lib/value_with_code.g.dart b/example/lib/value_with_code.g.dart
new file mode 100644
index 00000000..7faaa66e
--- /dev/null
+++ b/example/lib/value_with_code.g.dart
@@ -0,0 +1,61 @@
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+part of value_with_code;
+
+// **************************************************************************
+// Generator: BuiltValueGenerator
+// Target: abstract class ValueWithCode
+// **************************************************************************
+
+class _$ValueWithCode extends ValueWithCode {
+  final int anInt;
+  final String aString;
+
+  _$ValueWithCode._({this.anInt, this.aString}) : super._() {
+    if (anInt == null) throw new ArgumentError('null anInt');
+  }
+
+  factory _$ValueWithCode([updates(ValueWithCodeBuilder b)]) =>
+      (new ValueWithCodeBuilder()..update(updates)).build();
+
+  ValueWithCode rebuild(updates(ValueWithCodeBuilder b)) =>
+      (toBuilder()..update(updates)).build();
+
+  ValueWithCodeBuilder toBuilder() => new ValueWithCodeBuilder()..replace(this);
+
+  bool operator ==(other) {
+    if (other is! ValueWithCode) return false;
+    return anInt == other.anInt && aString == other.aString;
+  }
+
+  int get hashCode {
+    return hashObjects([anInt, aString]);
+  }
+
+  String toString() {
+    return 'ValueWithCode {'
+        'anInt=${anInt.toString()},\n'
+        'aString=${aString.toString()},\n'
+        '}';
+  }
+}
+
+class ValueWithCodeBuilder
+    implements Builder<ValueWithCode, ValueWithCodeBuilder> {
+  ValueWithCodeBuilder();
+  int anInt;
+  String aString;
+
+  void replace(ValueWithCode other) {
+    this.anInt = other.anInt;
+    this.aString = other.aString;
+  }
+
+  void update(updates(ValueWithCodeBuilder b)) {
+    if (updates != null) updates(this);
+  }
+
+  ValueWithCode build() {
+    return new _$ValueWithCode._(anInt: anInt, aString: aString);
+  }
+}
diff --git a/example/lib/value_with_defaults.dart b/example/lib/value_with_defaults.dart
new file mode 100644
index 00000000..c8130b00
--- /dev/null
+++ b/example/lib/value_with_defaults.dart
@@ -0,0 +1,42 @@
+// Copyright (c) 2016, Google Inc. Please see the AUTHORS file for details.
+// All rights reserved. Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+library value_with_defaults;
+
+import 'package:built_value/built_value.dart';
+
+part 'value_with_defaults.g.dart';
+
+/// Example of how to use built_value.
+///
+/// To provide defaults, write the builder as an explicit class instead of
+/// letting it be fully generated. See below.
+abstract class ValueWithDefaults
+    implements Built<ValueWithDefaults, ValueWithDefaultsBuilder> {
+  int get anInt;
+  @nullable
+  String get aString;
+
+  ValueWithDefaults._();
+  factory ValueWithDefaults([updates(ValueWithDefaultsBuilder b)]) =
+      _$ValueWithDefaults;
+}
+
+/// The builder class must implement [Builder]. It must be abstract, and have
+/// fields declared as normal public fields. Finally, it must have a particular
+/// constructor and factory, as shown here.
+///
+/// Defaults can be specified by assigning them to fields here.
+///
+/// You can further customize the builder by adding methods and setters
+/// and implementing interfaces.
+abstract class ValueWithDefaultsBuilder
+    implements Builder<ValueWithDefaults, ValueWithDefaultsBuilder> {
+  int anInt = 7;
+  @nullable
+  String aString;
+
+  ValueWithDefaultsBuilder._();
+  factory ValueWithDefaultsBuilder() = _$ValueWithDefaultsBuilder;
+}
diff --git a/example/lib/value_with_defaults.g.dart b/example/lib/value_with_defaults.g.dart
new file mode 100644
index 00000000..7072858e
--- /dev/null
+++ b/example/lib/value_with_defaults.g.dart
@@ -0,0 +1,58 @@
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+part of value_with_defaults;
+
+// **************************************************************************
+// Generator: BuiltValueGenerator
+// Target: abstract class ValueWithDefaults
+// **************************************************************************
+
+class _$ValueWithDefaults extends ValueWithDefaults {
+  final int anInt;
+  final String aString;
+
+  _$ValueWithDefaults._({this.anInt, this.aString}) : super._() {
+    if (anInt == null) throw new ArgumentError('null anInt');
+  }
+
+  factory _$ValueWithDefaults([updates(ValueWithDefaultsBuilder b)]) =>
+      (new ValueWithDefaultsBuilder()..update(updates)).build();
+
+  ValueWithDefaults rebuild(updates(ValueWithDefaultsBuilder b)) =>
+      (toBuilder()..update(updates)).build();
+
+  _$ValueWithDefaultsBuilder toBuilder() =>
+      new _$ValueWithDefaultsBuilder()..replace(this);
+
+  bool operator ==(other) {
+    if (other is! ValueWithDefaults) return false;
+    return anInt == other.anInt && aString == other.aString;
+  }
+
+  int get hashCode {
+    return hashObjects([anInt, aString]);
+  }
+
+  String toString() {
+    return 'ValueWithDefaults {'
+        'anInt=${anInt.toString()},\n'
+        'aString=${aString.toString()},\n'
+        '}';
+  }
+}
+
+class _$ValueWithDefaultsBuilder extends ValueWithDefaultsBuilder {
+  _$ValueWithDefaultsBuilder() : super._();
+  void replace(ValueWithDefaults other) {
+    super.anInt = other.anInt;
+    super.aString = other.aString;
+  }
+
+  void update(updates(ValueWithDefaultsBuilder b)) {
+    if (updates != null) updates(this);
+  }
+
+  ValueWithDefaults build() {
+    return new _$ValueWithDefaults._(anInt: anInt, aString: aString);
+  }
+}
diff --git a/example/pubspec.yaml b/example/pubspec.yaml
index c6877eda..e034eab9 100644
--- a/example/pubspec.yaml
+++ b/example/pubspec.yaml
@@ -1,5 +1,5 @@
 name: example
-version: 0.1.2
+version: 0.1.3
 description: >
   Just an example, not for publishing.
 authors:
@@ -11,8 +11,12 @@ environment:
 
 dependencies:
   built_collection: '^1.0.0'
-  built_value: '^0.1.2'
+#  built_value: '^0.1.3'
+  built_value:
+    path: ../built_value
 
 dev_dependencies:
-  built_value_generator: '^0.1.2'
+#  built_value_generator: '^0.1.3'
+  built_value_generator:
+    path: ../built_value_generator
   test: any
diff --git a/example/test/collections_test.dart b/example/test/collections_test.dart
new file mode 100644
index 00000000..c4de0266
--- /dev/null
+++ b/example/test/collections_test.dart
@@ -0,0 +1,74 @@
+// Copyright (c) 2016, Google Inc. 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.
+
+import 'package:built_collection/built_collection.dart';
+import 'package:example/collections.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('Collections', () {
+    test('can be instantiated', () {
+      new Collections();
+    });
+
+    test('default to empty if not nullable', () {
+      expect(new Collections().list.isEmpty, true);
+      expect(new Collections().set.isEmpty, true);
+      expect(new Collections().map.isEmpty, true);
+      expect(new Collections().listMultimap.isEmpty, true);
+      expect(new Collections().setMultimap.isEmpty, true);
+    });
+
+    test('default to null if nullable', () {
+      expect(new Collections().nullableList, null);
+      expect(new Collections().nullableSet, null);
+      expect(new Collections().nullableMap, null);
+      expect(new Collections().nullableListMultimap, null);
+      expect(new Collections().nullableSetMultimap, null);
+    });
+
+    test('can be updated via builder', () {
+      final collections = new Collections((b) => b
+        ..list.add(1)
+        ..set.add('two')
+        ..map['three'] = 4
+        ..listMultimap.add(5, true)
+        ..setMultimap.add('six', false));
+
+      expect(collections.list, [1]);
+      expect(collections.set, ['two']);
+      expect(collections.map.toMap(), {'three': 4});
+      expect(collections.listMultimap.toMap(), {
+        5: [true]
+      });
+      expect(collections.setMultimap.toMap(), {
+        'six': [false]
+      });
+    });
+
+    test('can be set from null via builder', () {
+      final collections = new Collections((b) => b
+        ..nullableList = new ListBuilder<int>()
+        ..nullableSet = new SetBuilder<String>()
+        ..nullableMap = new MapBuilder<String, int>()
+        ..nullableListMultimap = new ListMultimapBuilder<int, bool>()
+        ..nullableSetMultimap = new SetMultimapBuilder<String, bool>()
+        ..nullableList.add(1)
+        ..nullableSet.add('two')
+        ..nullableMap['three'] = 4
+        ..nullableListMultimap.add(5, true)
+        ..nullableSetMultimap.add('six', false));
+
+      expect(collections.nullableList, [1]);
+      expect(collections.nullableSet, ['two']);
+      expect(collections.nullableMap.toMap(), {'three': 4});
+      expect(collections.nullableListMultimap.toMap(), {
+        5: [true]
+      });
+      expect(collections.nullableSetMultimap.toMap(), {
+        'six': [false]
+      });
+    });
+  });
+}
diff --git a/example/test/compound_value_test.dart b/example/test/compound_value_test.dart
index 662133dc..3ec63204 100644
--- a/example/test/compound_value_test.dart
+++ b/example/test/compound_value_test.dart
@@ -3,20 +3,30 @@
 // license that can be found in the LICENSE file.
 
 import 'package:example/compound_value.dart';
+import 'package:example/validated_value.dart';
 import 'package:test/test.dart';
 
 void main() {
-  group('compound value', () {
+  group('CompoundValue', () {
     test('can be instantiated', () {
-      new CompoundValue();
+      new CompoundValue((b) => b..simpleValue.anInt = 1);
     });
 
     test('allows nested updates', () {
       expect(
-          new CompoundValue((b) => b.value
-            ..anInt = 1
-            ..anObject = 2).value.anInt,
+          new CompoundValue((b) => b
+            ..simpleValue.anInt = 1
+            ..simpleValue.aString = 'two').simpleValue.anInt,
           1);
     });
+
+    test('nullable nested builders can be assigned', () {
+      expect(
+          new CompoundValue((b) => b
+            ..simpleValue.anInt = 1
+            ..validatedValue = new ValidatedValueBuilder()
+            ..validatedValue.anInt = 2).validatedValue.anInt,
+          2);
+    });
   });
 }
diff --git a/example/test/simple_value_test.dart b/example/test/simple_value_test.dart
new file mode 100644
index 00000000..e196456c
--- /dev/null
+++ b/example/test/simple_value_test.dart
@@ -0,0 +1,95 @@
+// Copyright (c) 2016, Google Inc. 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.
+
+import 'package:example/simple_value.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('SimpleValue', () {
+    test('can be instantiated', () {
+      new SimpleValue((b) => b..anInt = 0);
+    });
+
+    test('throws on null for non-nullable fields on build', () {
+      expect(() => new SimpleValue(), throws);
+    });
+
+    test('throws on wrong type assign', () {
+      expect(() => new SimpleValue((b) => b..anInt = '0'), throws);
+    });
+
+    test('fields can be set via build constructor', () {
+      final value = new SimpleValue((b) => b
+        ..anInt = 1
+        ..aString = 'two');
+      expect(value.anInt, 1);
+      expect(value.aString, 'two');
+    });
+
+    test('fields can be updated via rebuild method', () {
+      final value = new SimpleValue((b) => b
+        ..anInt = 0
+        ..aString = '').rebuild((b) => b
+        ..anInt = 1
+        ..aString = 'two');
+      expect(value.anInt, 1);
+      expect(value.aString, 'two');
+    });
+
+    test('builder can be instantiated', () {
+      new SimpleValueBuilder();
+    });
+
+    test('compares equal when equal', () {
+      final value1 = new SimpleValue((b) => b
+        ..anInt = 0
+        ..aString = '');
+      final value2 = new SimpleValue((b) => b
+        ..anInt = 0
+        ..aString = '');
+      expect(value1, value2);
+    });
+
+    test('compares not equal when not equal', () {
+      final value1 = new SimpleValue((b) => b
+        ..anInt = 0
+        ..aString = '');
+      final value2 = new SimpleValue((b) => b
+        ..anInt = 1
+        ..aString = '');
+      expect(value1, isNot(equals(value2)));
+    });
+
+    test('hashes equal when equal', () {
+      final value1 = new SimpleValue((b) => b
+        ..anInt = 0
+        ..aString = '');
+      final value2 = new SimpleValue((b) => b
+        ..anInt = 0
+        ..aString = '');
+      expect(value1.hashCode, value2.hashCode);
+    });
+
+    test('hashes not equal when not equal', () {
+      final value1 = new SimpleValue((b) => b
+        ..anInt = 0
+        ..aString = '');
+      final value2 = new SimpleValue((b) => b
+        ..anInt = 1
+        ..aString = '');
+      expect(value1.hashCode, isNot(equals(value2.hashCode)));
+    });
+
+    test('has toString', () {
+      final value1 = new SimpleValue((b) => b
+        ..anInt = 0
+        ..aString = '');
+      expect(
+          value1.toString(),
+          '''SimpleValue {anInt=0,
+aString=,
+}''');
+    });
+  });
+}
diff --git a/example/test/validated_value_test.dart b/example/test/validated_value_test.dart
new file mode 100644
index 00000000..f7af63cf
--- /dev/null
+++ b/example/test/validated_value_test.dart
@@ -0,0 +1,18 @@
+// Copyright (c) 2015, Google Inc. 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.
+
+import 'package:example/validated_value.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('ValidatedValue', () {
+    test('can be instantiated', () {
+      new ValidatedValue((b) => b..anInt = 1);
+    });
+
+    test('does custom validation', () {
+      expect(() => new ValidatedValue((b) => b..anInt = 7), throws);
+    });
+  });
+}
diff --git a/example/test/value_test.dart b/example/test/value_test.dart
deleted file mode 100644
index d3f9c153..00000000
--- a/example/test/value_test.dart
+++ /dev/null
@@ -1,152 +0,0 @@
-// Copyright (c) 2015, Google Inc. 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.
-
-import 'package:built_collection/built_collection.dart';
-import 'package:example/value.dart';
-import 'package:test/test.dart';
-
-void main() {
-  group('value', () {
-    test('can be instantiated', () {
-      new Value((b) => b
-        ..anInt = 0
-        ..aString = '');
-    });
-
-    test('can be instantiated via custom factory', () {
-      expect(
-          new Value.fromCustomFactory(),
-          new Value((b) => b
-            ..anInt = 1
-            ..aString = 'two'));
-    });
-
-    test('has defaults', () {
-      expect(
-          new Value((b) => b
-            ..anInt = 0
-            ..aString = '').aDefaultInt,
-          7);
-    });
-
-    test('throws on null for non-nullable fields on build', () {
-      expect(() => new Value(), throws);
-    });
-
-    test('throws on wrong type assign', () {
-      expect(
-          () => new Value((b) => b
-            ..anInt = '0'
-            ..aString = ''),
-          throws);
-    });
-
-    test('does custom validation', () {
-      expect(
-          () => new Value((b) => b
-            ..anInt = 7
-            ..aString = ''),
-          throws);
-    });
-
-    test('fields can be set via build constructor', () {
-      final value = new Value((b) => b
-        ..anInt = 1
-        ..aString = 'two'
-        ..anObject = 3);
-      expect(value.anInt, 1);
-      expect(value.aString, 'two');
-      expect(value.anObject, 3);
-    });
-
-    test('fields can be updated via rebuild method', () {
-      final value = new Value((b) => b
-        ..anInt = 0
-        ..aString = '').rebuild((b) => b
-        ..anInt = 1
-        ..aString = 'two'
-        ..anObject = 3);
-      expect(value.anInt, 1);
-      expect(value.aString, 'two');
-      expect(value.anObject, 3);
-    });
-
-    test('builder can be instantiated', () {
-      new ValueBuilder();
-    });
-
-    test('collections can be updated using builder', () {
-      final value = new Value((b) => b
-        ..anInt = 1
-        ..aString = 'two'
-        ..listOfInt.update((b) => b
-          ..addAll([3, 2, 1])
-          ..sort()));
-      expect(value.listOfInt, [1, 2, 3]);
-    });
-
-    test('nullable builders can be updated', () {
-      final value = new Value((b) => b
-        ..anInt = 1
-        ..aString = 'two'
-        ..setOfString = new SetBuilder<String>(['1', '2', '3']));
-      expect(value.setOfString, ['1', '2', '3']);
-    });
-
-    test('compares equal when equal', () {
-      final value1 = new Value((b) => b
-        ..anInt = 0
-        ..aString = '');
-      final value2 = new Value((b) => b
-        ..anInt = 0
-        ..aString = '');
-      expect(value1, value2);
-    });
-
-    test('compares not equal when not equal', () {
-      final value1 = new Value((b) => b
-        ..anInt = 0
-        ..aString = '');
-      final value2 = new Value((b) => b
-        ..anInt = 1
-        ..aString = '');
-      expect(value1, isNot(equals(value2)));
-    });
-
-    test('hashes equal when equal', () {
-      final value1 = new Value((b) => b
-        ..anInt = 0
-        ..aString = '');
-      final value2 = new Value((b) => b
-        ..anInt = 0
-        ..aString = '');
-      expect(value1.hashCode, value2.hashCode);
-    });
-
-    test('hashes not equal when not equal', () {
-      final value1 = new Value((b) => b
-        ..anInt = 0
-        ..aString = '');
-      final value2 = new Value((b) => b
-        ..anInt = 1
-        ..aString = '');
-      expect(value1.hashCode, isNot(equals(value2.hashCode)));
-    });
-
-    test('has toString', () {
-      final value1 = new Value((b) => b
-        ..anInt = 0
-        ..aString = '');
-      expect(
-          value1.toString(),
-          '''Value {anInt=0
-aString=
-anObject=null
-aDefaultInt=7
-listOfInt=[]
-setOfString=null
-}''');
-    });
-  });
-}
diff --git a/example/test/value_with_code_test.dart b/example/test/value_with_code_test.dart
new file mode 100644
index 00000000..2346c9b2
--- /dev/null
+++ b/example/test/value_with_code_test.dart
@@ -0,0 +1,26 @@
+// Copyright (c) 2016, Google Inc. 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.
+
+import 'package:example/value_with_code.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('ValueWithCode', () {
+    test('can be instantiated via custom factory', () {
+      expect(
+          new ValueWithCode.fromCustomFactory(12),
+          new ValueWithCode((b) => b
+            ..anInt = 12
+            ..aString = 'two'));
+    });
+
+    test('has derived getter', () {
+      expect(
+          new ValueWithCode((b) => b
+            ..anInt = 12
+            ..aString = 'two').youCanWriteDerivedGetters,
+          '12two');
+    });
+  });
+}
diff --git a/example/test/value_with_defaults_test.dart b/example/test/value_with_defaults_test.dart
new file mode 100644
index 00000000..e8129333
--- /dev/null
+++ b/example/test/value_with_defaults_test.dart
@@ -0,0 +1,14 @@
+// Copyright (c) 2016, Google Inc. 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.
+
+import 'package:example/value_with_defaults.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('ValueWithDefaults', () {
+    test('has defaults', () {
+      expect(new ValueWithDefaults().anInt, 7);
+    });
+  });
+}