sum_data_types

Description:

sum data types

Sum Types and Data Classes for Dart #

This dart library generates immutable data classes and classes for sum types from
a blueprint mixin. The generated class define structural equality and hashCode. They
also provide a meaningful implementation of toString.
Also see this issue.
The library is influence by the data_classes
and the sum_types
libraries. However, their interfaces are different, so we created a new package.
Installation #
Add these packages to your dependencies:
dependencies:
sum_data_types: [insert newest version here]

dev_dependencies:
build_runner: ^1.7.0
sum_data_types_generator: [insert newest version here]
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Data Classes #
A data class is similar to an immutable record. The fields of a data class are used to define
equality and hashCode in a structural way.
Define a blueprint mixin #
Here is an example:
import 'package:sum_data_types/main.dart';
import 'package:quiver/core.dart';
import 'package:kt_dart/collection.dart';

@DataClass()
mixin User on _UserBase {
String get name;
Optional<int> get age;
KtList<User> get friends;

int numerOfFriends() {
return this.friends.size;
}
}
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The @DataClass() annotation triggers generation of the data class from the mixin
following the annotation.
The mixin should define getters for each property of the data class. The code generation
then generates code for == (structural equality), hashCode and toString.
Additionally, it generates
a copyWith method through which you can non-destructively modify some fields of an existing
object of the class (i.e. copyWith returns a copy of the object).
You can customize the code generation by using the two boolean flags toString and
eqHashCode. If you set one of the flags to false, then no code for toString or == and
hashCode, respectively, is generated. Example:
@DataClass(toString: false)
mixin UserWithPassword {
String get userId;
String get password;

String toString() {
return "User($userId)"; // do not print the password
}
}
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Use the generated class #
You create instances of the data class by using the static make method of the
also generated UserFactory class.
void main() {
final userBob = UserFactory.make(
name: "Bob",
friends: KtList.empty(),
);
final userSarah = UserFactory.make(
name: "Sarah",
friends: KtList.empty(userBob),
age: 31,
);
}
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Optional fields #
Fields are optional if their type is Optional<...>, where Optional comes from
the quiver.core library.
It is recommended to use immutable collections, for example from the
kt.dart package. You can also use the builtin collections
such as `List``, but their equality is based on pointer-equality and not on structural equality.
Sum Types #
A sum type combines various alternatives of types under a new type. The generated code
defines switching functiosn for distinguishing between the different alternatives.
Define a blueprint mixin #
Here is an example:
import 'package:sum_data_types/main.dart';

@SumType()
mixin Either<A, B> on _EitherBase<A, B> {
A get _left;
B get _right;
}
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The @SumType() annotation triggers generation of the data class from the mixin
following the annotation.
The mixin should define getters for each alternative of the sum type. The name
of the getters must start with an underscore. The code generation
then generates code for == (structural equality), hashCode and toString.
Additionally, it generates
iswitch and iswitcho methods which you can use to switch over the various alternatives.
Here is an example use of the iswitch method:
void foo(Either<String, int> x) {
x.iswitch(
left: (s) => print("String: " + s),
right: (i) => print("int: " + i.toString())
);
}
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The iswitcho method has an additional otherwise label, so you do not have to cover
all cases when using iswitcho.
You can customize the code generation by using the two boolean flags toString and
eqHashCode. If you set one of the flags to false, then no code for toString or == and
hashCode, respectively, is generated.
Use the generated class #
You create instances of the data class by using the static left and right methods of the
also generated EitherFactor class.
EitherFactory.right(42)
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