This package provides a common interface for initialization annotations on top level methods, classes, and libraries. The interface looks like this:

abstract class Initializer<T> {
  dynamic initialize(T target);

The initialize method will be called once for each annotation. The type T is determined by what was annotated. For libraries it will be the Symbol representing that library, for a class it will be the Type representing that class, and for a top level method it will be the Function object representing that method.

If a future is returned from the initialize method, it will wait until the future completes before running the next initializer.



Ther is one initializer which comes with this package, @initMethod. Annotate any top level function with this and it will be invoked automatically. For example, the program below will print hello:

import 'package:initialize/initialize.dart';

printHello() => print('hello');

main() => run();

Running the initializers

In order to run all the initializers, you need to import package:initialize/initialize.dart and invoke the run method. This should typically be the first thing to happen in your main. That method returns a Future, so you should put the remainder of your program inside the chained then call.

import 'package:initialize/initialize.dart';

main() {
  run().then((_) {
    print('hello world!');


During development a mirror based system is used to find and run the initializers, but for deployment there is a transformer which can replace that with a static list of initializers to be ran.

This transformer does not modify your existing files, but instead creates a new entrypoint which bootstraps your existing app. Below is an example pubspec with the transformer:

name: my_app
  initialize: any
- initialize:
    entryPoint: web/index.dart
    newEntryPoint: web/index.bootstrap.dart

Note: Until is resolved, it is necessary to rewrite any script tags pointing to your entry point to the new bootstrapped entry point manually.

Creating your own initializer

Lets look at a slightly simplified version of the @initMethod class:

class InitMethod implements Initializer<Function> {
  const InitMethod();

  initialize(Function method) => method();

You would now be able to add @InitMethod() in front of any function and it will be automatically invoked when the user calls run().

For classes which are stateless, you can usually just have a single const instance, and that is how the actual InitMethod implementation works. Simply add something like the following:

const initMethod = const InitMethod();

Now when people use the annotation, it just looks like @initMethod without any parenthesis, and its a bit more efficient since there is a single instance. You can also make your class private to force users into using the static instance.