select 0.1.0

Code generation for selectors of class fields that helps reduce repetitive code.

select

Code generation for selectors of class fields that helps reduce repetitive code.

Index

• Index
• About
• Motivation
• Install
  • Used packages
  • Pubspec
• Usage
  • Selectable class
  • Examples
    • Iterable
    • Stream
    • Provider
    • Selector builder

About

select helps generate selector methods for any class that can be used anywhere where you would use a selector-lambda. Only one annotation is used, and only one annotation is needed – every class annotated with @selectable would have selectors for all fields and all fields of applied mixins.

This package is compatible with the amazing freezed code generator.

Motivation

Selectors are widely used in Flutter and Dart. The most common places of usage are:

• Iterable transformations and especially mappings
• Stream transformations
• The select method extension from Provider
• Most of the selector-widgets, such as BlocSelector

Selector functions tend to be very repetitive, in the example function (state) => state.field, word state is repeated two times, and there are four symbols and two spaces. Overall, from 22 symbols, only 11 have a meaning, that is – state.field.

That's a great task for automation, and that's exactly what that package does. So instead of writing (model) => model.field, it is possible to write Model$.field with select.

Install

select is a code-generation package, so the typical generator-annotation-builder setup is used.

Used packages

• Generator – select
• Annotations – select_annotation
• Builder – build_runner

Pubspec

And the pubspec.yaml should be extended as in following:

dependencies:
  freezed_annotation: ^0.1.0

dev_dependencies:
  build_runner: #latest version
  select: ^0.1.0

Usage

To generate selectors for a class, two following criteria should be met:

1. The class is marked with the @selectable annotation.
2. File with the class includes a generated code, part model.select.dart;.

Selectable class

The following example demonstrates a minimal useful definition of the selectable class.

import 'package:select_annotation/select_annotation.dart';

part 'user.select.dart';

@selectable
class User {
  final String name;
  final int age;

  const User(this.name, this.age);
}

selectable can (and probably should) be used in conjunction with the freezed generator and other annotations.

import 'package:select_annotation/select_annotation.dart';
import 'package:freezed_annotation/freezed_annotation.dart';

part 'user.select.dart';
part 'user.freezed.dart';

@selectable
@immutable
@freezed
class User with _$User {
  const factory User(String name, int age) = _User;
}

With the given User model, a class with two static methods will be generated.

abstract class User$ {
  User$._();

  static String name(User user) => user.name;
  static int age(User user) => user.age;
}

And that's it – those selectors can be used in any way, that a regular anonymous selector is used.

Examples

Down below are listed the most commonly used use-cases for selectors and their versions implemented with selectable.

Iterable

[User('Bob', 28)].map(User$.name);

Stream

Stream.fromIterable([User('Jade', 33)]).map(User$.age);

Provider

Widget build(BuildContext context) {
  final userName = context.select(User$.name);
  
  return ...;
}

Selector builder

Widget build(BuildContext context) => BlocSelector<UserBloc, UserModel, int>(
  selector: User$.age
  builder: ...,
);