commit | a9ef4857450f251adf6ab418484cec503c6b1d44 | [log] [tgz] |
---|---|---|
author | Felix Angelov <felangelov@gmail.com> | Mon Jun 14 16:41:57 2021 -0500 |
committer | GitHub <noreply@github.com> | Mon Jun 14 16:41:57 2021 -0500 |
tree | bae539a56ac023a1c14bdb2133a77a8b14a05162 | |
parent | a5c9ac00e5562e8dcc90ac5ca505b25daa7ee99a [diff] |
chore(deps): remove unused coverage dev dependency (#125)
Being able to compare objects in Dart
often involves having to override the ==
operator as well as hashCode
.
Not only is it verbose and tedious, but failure to do so can lead to inefficient code which does not behave as we expect.
By default, ==
returns true if two objects are the same instance.
Let's say we have the following class:
class Person { const Person(this.name); final String name; }
We can create create instances of Person
like so:
void main() { final Person bob = Person("Bob"); }
Later if we try to compare two instances of Person
either in our production code or in our tests we will run into a problem.
print(bob == Person("Bob")); // false
For more information about this, you can check out the official Dart Documentation.
In order to be able to compare two instances of Person
we need to change our class to override ==
and hashCode
like so:
class Person { const Person(this.name); final String name; @override bool operator ==(Object other) => identical(this, other) || other is Person && runtimeType == other.runtimeType && name == other.name; @override int get hashCode => name.hashCode; }
Now if we run the following code again:
print(bob == Person("Bob")); // true
it will be able to compare different instances of Person
.
You can see how this can quickly become a hassle when dealing with complex classes. This is where Equatable
comes in!
Equatable
overrides ==
and hashCode
for you so you don't have to waste your time writing lots of boilerplate code.
There are other packages that will actually generate the boilerplate for you; however, you still have to run the code generation step which is not ideal.
With Equatable
there is no code generation needed and we can focus more on writing amazing applications and less on mundane tasks.
First, we need to do add equatable
to the dependencies of the pubspec.yaml
dependencies: equatable: ^2.0.0
Next, we need to install it:
# Dart pub get # Flutter flutter packages get
Lastly, we need to extend Equatable
import 'package:equatable/equatable.dart'; class Person extends Equatable { const Person(this.name); final String name; @override List<Object> get props => [name]; }
When working with json:
import 'package:equatable/equatable.dart'; class Person extends Equatable { const Person(this.name); final String name; @override List<Object> get props => [name]; factory Person.fromJson(Map<String, dynamic> json) { return Person(json['name']); } }
We can now compare instances of Person
just like before without the pain of having to write all of that boilerplate. Note: Equatable is designed to only work with immutable objects so all member variables must be final (This is not just a feature of Equatable
- overriding a hashCode
with a mutable value can break hash-based collections).
Equatable also supports const
constructors:
import 'package:equatable/equatable.dart'; class Person extends Equatable { const Person(this.name); final String name; @override List<Object> get props => [name]; }
toString
ImplementationEquatable can implement toString
method including all the given props. If you want that behaviour for a specific Equatable
object, just include the following:
@override bool get stringify => true;
For instance:
import 'package:equatable/equatable.dart'; class Person extends Equatable { const Person(this.name); final String name; @override List<Object> get props => [name]; @override bool get stringify => true; }
For the name Bob
, the output will be:
Person(Bob)
This flag by default is false and toString
will return just the type:
Person
stringify
can also be configured globally for all Equatable
instances via EquatableConfig
EquatableConfig.stringify = true;
If stringify
is overridden for a specific Equatable
class, then the value of EquatableConfig.stringify
is ignored. In other words, the local configuration always takes precedence over the global configuration.
Note: EquatableConfig.stringify
defaults to true
in debug mode and false
in release mode.
class Person { const Person(this.name); final String name; @override bool operator ==(Object other) => identical(this, other) || other is Person && runtimeType == other.runtimeType && name == other.name; @override int get hashCode => name.hashCode; }
import 'package:equatable/equatable.dart'; class Person extends Equatable { const Person(this.name); final String name; @override List<Object> get props => [name]; }
Sometimes it isn't possible to extend Equatable
because your class already has a superclass. In this case, you can still get the benefits of Equatable
by using the EquatableMixin
.
Let's say we want to make an EquatableDateTime
class, we can use EquatableMixin
like so:
class EquatableDateTime extends DateTime with EquatableMixin { EquatableDateTime( int year, [ int month = 1, int day = 1, int hour = 0, int minute = 0, int second = 0, int millisecond = 0, int microsecond = 0, ]) : super(year, month, day, hour, minute, second, millisecond, microsecond); @override List<Object> get props { return [year, month, day, hour, minute, second, millisecond, microsecond]; } }
Now if we want to create a subclass of EquatableDateTime
, we can just override props
.
class EquatableDateTimeSubclass extends EquatableDateTime { final int century; EquatableDateTimeSubclass( this.century, int year,[ int month = 1, int day = 1, int hour = 0, int minute = 0, int second = 0, int millisecond = 0, int microsecond = 0, ]) : super(year, month, day, hour, minute, second, millisecond, microsecond); @override List<Object> get props => super.props..addAll([century]); }
You might be wondering what the performance impact will be if you use Equatable
.
Class | Runtime (μs) |
---|---|
Manual | 0.193 |
Empty Equatable | 0.191 |
Hydrated Equatable | 0.190 |
Class | Runtime (μs) |
---|---|
Manual | 0.165 |
Empty Equatable | 0.181 |
Hydrated Equatable | 0.182 |
*Performance Tests run using: Dart VM version: 2.4.0