jennsenr/dart-union-generator

Union Generator

What inspired us?

We've been really happy using freezed package tool to create our union classes, which have given us the possibility of having a better solution than common enums, providing methods like map, when, maybeMap and maybeWhen that allowed us to avoid omissions when working with different possible enumerated values for an instance.

So, what's the problem? Well... Freezed package creates auto-generated code and this, of course, makes stuff to be impossible to control, while adds some extra dependencies that we wanted to avoid at all.

Now, we're going to explain how to use the extension, so you can have full control on your code while easily having all the advantajes that unions give us.

Usage

This extension works by creating a template class that will help us know what to generate next. The expected structure is as follows:

class YourClassName{
    const factory YourClassName.firstUseCase() = NameForFirstUseCaseClass;
    const factory YourClassName.secondUseCase(String arg1, int arg2, bool arg 3) = NameForSecondUseCaseClass;
    const factory YourClassName.thirdUseCase(String arg1) = NameForThirdUseCaseClass;
}

This example will generate a type YourClassName which can be of any of these subtypes:

NameForFirstUseCaseClass || NameForSecondUseCaseClass || NameForThirdUseCaseClass

Also, this will provide you the handy methods map, when, maybeMap and maybeWhen.

To activate generation you must place the cursor in the class declaration line, and press cntrl (cmd) + .

Why would I use Unions?

This is a perfect solution since you don't need to remember every single possible value that an instance can have, as the provided methods will handle this task themselves.

What to do if you can't generate the Unions

Here we'll describe some cases where you could have some troubles trying to use the extension.

First of all, as it's on a very early stage, some cases are not (yet) supported:

• Dart version < 2.12.0. You'll need to upgrade to (at least) dart version 2.12.0 so you can use this extension.

Support

We highly encourage you to create a pull request for this extension if you want to improve it. Your help is always welcome. Also, you can open issues if there's any trouble.

dart-union-generator's Issues

Override hashcode and equality operator

Add support for generics

Add getters for union cases

Port to Android Studio

Add support for legacy Dart < 2.12.0

Add method syntax

description:

a shorter syntax is proposed, like:

class ExampleUnion {
  UnionCaseOne();
  UnionCaseTwo(String message);
}

instead of:

class ExampleUnion {
  factory ExampleUnion.unionCaseOne() = UnionCaseOne;
  factory ExampleUnion.unionCaseTwo(String message) = UnionCaseTwo;
}

motivation:

• write less to improve productivity

implication:

• current syntax support must be maintained.
• the generated code must be the same with both syntax

Add const constructors

Add maybe methods

currently exist map and when, maybe Map and maybeWhen should be added.

these methods must receive an orElse callback that is called in case the corresponding callback case is null

Stop execution in maybeWhen methods

Should not remove imports

Add value getter

This getter should return the union class value in string.

Do not generate the fromString if there are cases with arguments

Allow implement abstract class or mixin

Syntax changes

Change factories syntax

from:

factory ServerErrorFailure.unknown() => ServerErrorFailureUnknown();
factory ServerErrorFailure.invalidArgument(String message, int code) =>
ServerErrorFailureInvalidArgument(message, code);

to:

factory ServerErrorFailure.unknown() = ServerErrorFailureUnknown;
factory ServerErrorFailure.invalidArgument(String message, int code) = ServerErrorFailureInvalidArgument;

Make private the union classes by default

Should not remove custom methods

Add documentation

Add fromString/toString methods

Add setting for snake_case value getter

Add tests