Implement toString feature

README.md

@@ -166,6 +166,39 @@ class Person extends Equatable {
 }
 ```
 
+### `toString` Implementation
+Equatable can implement `toString` method including all the given props. If you want that behaviour, just include the following:
+```
+  @override
+  bool get stringify => true;
+```
+
+For instance:
+
+```dart
+import 'package:equatable/equatable.dart';
+
+class Person extends Equatable {
+  final String name;
+
+  const Person(this.name);
+
+  @override
+  List<Object> get props => [name];
+
+  @override
+  bool get stringify => true;
+}
+```
+For the name `Bob`, the outuput will be:
+```
+Person(Bob)
+```
+This flag by default is false and `toString` will return just the type:
+```
+Person
+```
+
 ## Recap
 
 ### Without Equatable

example/main.dart

@@ -8,6 +8,9 @@ class Credentials extends Equatable {
 
   @override
   List<Object> get props => [username, password];
+
+  @override
+  bool get stringify => false;
 }
 
 class EquatableDateTime extends DateTime with EquatableMixin {
@@ -26,6 +29,9 @@ class EquatableDateTime extends DateTime with EquatableMixin {
   List get props {
     return [year, month, day, hour, minute, second, millisecond, microsecond];
   }
+
+  @override
+  bool get stringify => true;
 }
 
 void main() {
@@ -39,6 +45,7 @@ void main() {
   print(credentialsC == credentialsC); // true
   print(credentialsA == credentialsB); // false
   print(credentialsB == credentialsC); // true
+  print(credentialsA.toString()); // Credentials
 
   // Equatable Mixin
   final dateTimeA = EquatableDateTime(2019);
@@ -50,4 +57,5 @@ void main() {
   print(dateTimeC == dateTimeC); // true
   print(dateTimeA == dateTimeB); // false
   print(dateTimeB == dateTimeC); // true
+  print(dateTimeA.toString()); // EquatableDateTime(2019, 1, 1, 0, 0, 0, 0, 0)
 }

lib/src/equatable.dart

@@ -1,4 +1,5 @@
 import 'package:meta/meta.dart';
+
 import './equatable_utils.dart';
 
 /// A base class to facilitate [operator==] and [hashCode] overrides.
@@ -19,6 +20,10 @@ abstract class Equatable {
   /// two [Equatables] are equal.
   List<Object> get props;
 
+  /// If the value is [true], the `toString` method will be overrided to print
+  /// the equatable `props`.
+  bool get stringify => false;
+
   /// A class that helps implement equality
   /// without needing to explicitly override == and [hashCode].
   /// Equatables override their own `==` operator and [hashCode] based on their `props`.
@@ -35,5 +40,6 @@ abstract class Equatable {
   int get hashCode => runtimeType.hashCode ^ mapPropsToHashCode(props);
 
   @override
-  String toString() => '$runtimeType';
+  String toString() =>
+      stringify ? mapPropsToString(runtimeType, props) : '$runtimeType';
 }

lib/src/equatable_mixin.dart

@@ -9,6 +9,10 @@ mixin EquatableMixin {
   /// two [Equatables] are equal.
   List<Object> get props;
 
+  /// If the value is [true], the `toString` method will be overrided to print
+  /// the equatable `props`.
+  bool get stringify => false;
+
   @override
   bool operator ==(Object other) {
     return identical(this, other) ||
@@ -21,5 +25,6 @@ mixin EquatableMixin {
   int get hashCode => runtimeType.hashCode ^ mapPropsToHashCode(props);
 
   @override
-  String toString() => '$runtimeType';
+  String toString() =>
+      stringify ? mapPropsToString(runtimeType, props) : '$runtimeType';
 }

lib/src/equatable_utils.dart

@@ -1,7 +1,7 @@
 import 'package:collection/collection.dart';
 
 int mapPropsToHashCode(Iterable props) =>
-    _finish(props.fold(0, (hash, object) => _combine(hash, object)));
+    _finish(props?.fold(0, (hash, object) => _combine(hash, object)) ?? 0);
 
 const DeepCollectionEquality _equality = DeepCollectionEquality();
 
@@ -47,3 +47,6 @@ int _finish(int hash) {
   hash = hash ^ (hash >> 11);
   return 0x1fffffff & (hash + ((0x00003fff & hash) << 15));
 }
+
+String mapPropsToString(Type runtimeType, List<Object> props) =>
+    '$runtimeType${props?.map((prop) => prop?.toString() ?? '') ?? '()'}';

test/equatable_mixin_test.dart

@@ -1,8 +1,8 @@
 import 'dart:convert';
 
+import 'package:equatable/equatable.dart';
 import 'package:equatable/src/equatable_utils.dart';
 import 'package:test/test.dart';
-import 'package:equatable/equatable.dart';
 
 class NonEquatable {}
 
@@ -89,6 +89,30 @@ class Credentials extends EquatableBase {
   }
 }
 
+class ComplexStringify extends ComplexEquatable {
+  final String name;
+  final int age;
+  final Color hairColor;
+
+  ComplexStringify({this.name, this.age, this.hairColor});
+
+  @override
+  List get props => [name, age, hairColor];
+
+  @override
+  bool get stringify => true;
+}
+
+class NullProps extends Equatable {
+  NullProps();
+
+  @override
+  List get props => null;
+
+  @override
+  bool get stringify => true;
+}
+
 void main() {
   group('Empty Equatable', () {
     test('should correct toString', () {
@@ -546,4 +570,35 @@ void main() {
       expect(instanceA == instanceB, false);
     });
   });
+
+  group('To String Equatable', () {
+    test('Complex stringify', () {
+      final instanceA = ComplexStringify();
+      final instanceB = ComplexStringify(name: "Bob", hairColor: Color.black);
+      final instanceC =
+          ComplexStringify(name: "Joe", age: 50, hairColor: Color.blonde);
+      expect(instanceA.toString(), 'ComplexStringify(, , )');
+      expect(instanceB.toString(), 'ComplexStringify(Bob, , Color.black)');
+      expect(instanceC.toString(), 'ComplexStringify(Joe, 50, Color.blonde)');
+    });
+  });
+
+  group('Null props Equatable', () {
+    test('should not crash invoking equals method', () {
+      final instanceA = NullProps();
+      final instanceB = NullProps();
+      expect(instanceA == instanceB, true);
+    });
+
+    test('should not crash invoking hascode method', () {
+      final instanceA = NullProps();
+      final instanceB = NullProps();
+      expect(instanceA.hashCode == instanceB.hashCode, true);
+    });
+
+    test('should not crash invoking toString method', () {
+      final instance = NullProps();
+      expect(instance.toString(), 'NullProps()');
+    });
+  });
 }

test/equatable_test.dart

@@ -1,10 +1,9 @@
 import 'dart:convert';
 
+import 'package:equatable/equatable.dart';
 import 'package:equatable/src/equatable_utils.dart';
 import 'package:test/test.dart';
 
-import 'package:equatable/equatable.dart';
-
 import 'custom_list.dart';
 
 class NonEquatable {}
@@ -92,6 +91,30 @@ class Credentials extends Equatable {
   List<Object> get props => [username, password];
 }
 
+class ComplexStringify extends Equatable {
+  final String name;
+  final int age;
+  final Color hairColor;
+
+  ComplexStringify({this.name, this.age, this.hairColor});
+
+  @override
+  List get props => [name, age, hairColor];
+
+  @override
+  bool get stringify => true;
+}
+
+class NullProps extends Equatable {
+  NullProps();
+
+  @override
+  List get props => null;
+
+  @override
+  bool get stringify => true;
+}
+
 void main() {
   group('Empty Equatable', () {
     test('should correct toString', () {
@@ -721,6 +744,37 @@ void main() {
       });
     });
   });
+
+  group('To String Equatable', () {
+    test('with Complex stringify', () {
+      final instanceA = ComplexStringify();
+      final instanceB = ComplexStringify(name: "Bob", hairColor: Color.black);
+      final instanceC =
+          ComplexStringify(name: "Joe", age: 50, hairColor: Color.blonde);
+      expect(instanceA.toString(), 'ComplexStringify(, , )');
+      expect(instanceB.toString(), 'ComplexStringify(Bob, , Color.black)');
+      expect(instanceC.toString(), 'ComplexStringify(Joe, 50, Color.blonde)');
+    });
+  });
+
+  group('Null props Equatable', () {
+    test('should not crash invoking equals method', () {
+      final instanceA = NullProps();
+      final instanceB = NullProps();
+      expect(instanceA == instanceB, true);
+    });
+
+    test('should not crash invoking hascode method', () {
+      final instanceA = NullProps();
+      final instanceB = NullProps();
+      expect(instanceA.hashCode == instanceB.hashCode, true);
+    });
+
+    test('should not crash invoking toString method', () {
+      final instance = NullProps();
+      expect(instance.toString(), 'NullProps()');
+    });
+  });
 }
 
 // test that subclasses of `Equatable` can have const constructors