Skip to content

Fix Lazy Initialization #1644

Open
Open
@NullVoxPopuli

Description

@NullVoxPopuli

Problem: @tracked is eagerly consumed when we don't want it to be

Broken:

import Component from '@glimmer/component';
import { tracked } from '@glimmer/tracking';

let _id = 0;

function id() {
  return _id++;
}

/**
  *
  * Expected: 1, 2, 3, 4, 3, 4, 5, 6, 7
  * Actual: 1, 2, 3, 4, <Error>
  *
  * Observation:
  *  - Sub's constructor may be entangled with Outer#collection
  *
  */

class Sub extends Component {
  constructor(...args) {
    super(...args);
    console.log(3);
    this.args.register(id());
  }
  <template></template>
}

class Outer extends Component {
  @tracked collection = [];

  register = (id) => {
    console.log(4);
    this.collection.push(id);
    this.collection = this.collection;
  };

  <template>
    {{log 1}}
    {{yield (component Sub register=this.register)}}
    {{log 6}}

    {{! (read collection the first time) }}
    {{log 7}}
    {{#each this.collection as |item|}}
      {{item}}
    {{/each}}
  </template>
}

<template>
  <Outer as |Sub|>
    {{log 2}}
    <Sub />
    <Sub />
    {{log 5}}
  </Outer>
</template>

Works:

import Component from '@glimmer/component';
import { tracked } from '@glimmer/tracking';

import {
  createStorage,
  getValue,
  setValue,
} from 'ember-tracked-storage-polyfill';

let _id = 0;

function id() {
  return _id++;
}

/**
  *
  * Expected: 1, 2, 3, 4, 3, 4, 5, 6, 7
  * Actual: 1, 2, 3, 4, 5, 6, 7
  *
  */

class Sub extends Component {
  constructor(...args) {
    super(...args);
    console.log(3);
    this.args.register(id());
  }
  <template></template>
}

class Outer extends Component {
  _collection;
  get collection() {
    if (!this._collection) {
      this._collection = createStorage([]);
    }

    return getValue(this._collection);
  }
  set collection(value) {
    setValue(this._collection, value);
  }

  register = (id) => {
    console.log(4);
    this.collection.push(id);
    this.collection = this.collection;
  };

  <template>
    {{log 1}}
    {{yield (component Sub register=this.register)}}
    {{log 6}}

    {{! (read collection the first time) }}
    {{log 7}}
    {{#each this.collection as |item|}}
      {{item}}
    {{/each}}
  </template>
}

<template>
  <Outer as |Sub|>
    {{log 2}}
    <Sub />
    <Sub />
    {{log 5}}
  </Outer>
</template>

Metadata

Metadata

Assignees

No one assigned

    Labels

    No labels
    No labels

    Type

    No type

    Projects

    No projects

    Milestone

    No milestone

    Relationships

    None yet

    Development

    No branches or pull requests

    Issue actions