compiled_mirrors 0.1.0

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Compiled Mirrors #

Statically reflecting Dart classes.

Reflection in Dart through dart:mirrors is a powerful tool for building tests and assorted utilities. However, when compiled to JavaScript and run in a browser, mirrors can severely reduce code's performance. In Flutter, mirrors are disabled entirely.

Compiled Mirrors generates a reflection of Dart classes annotated with @compileMirrors. This allows you to do a number of interesting things.

Testing complex classes #

My focus has been on using this as a testing utility for evaluating the fields between two complex objects. For example, suppose we have the following class:

class Person {
  final String firstName;
  final String lastName;
  final int age;
  final Location birthplace;
  final Location residence;
  final University almaMater;

  Person(this.firstName, this.lastName, this.gender, this.age,
      this.birthplace, this.residence, this.almaMater);

  factory Person.fromParents(Person mother, Person father) {
    // Make a new person with traits of both parents.

Suppose we want to test the fromParents factory. We'd need to build an expected Person for the results of the test, and an actual Person:

test('fromParents Person factory', () {
  var expected = new Person(/* various fields */);
  var actual = new Person.fromParents(testMother, testFather);

Without an equality definition for this person, we need to test against every field in the Person object:

  expect(actual.firstName, expected.firstName);
  expect(actual.lastName, expected.lastName);
  // boilerplate continues.

Very verbose!

Also, if we decide later on that we want to add a birthDate field to Person, the test will pass even if the factory generates a birthDate we didn't expect! This is a bug waiting to happen.

Mirrored fields #

We can avoid this problem with a mirror of the object's fields. If we compile a mirror for the Person object, we can generate an automatically-updating equality test:

test('fromParents Person factory', () {
  var expected = new Person(/* various fields */);
  var actual = new Person.fromParents(testMother, testFather);
  var expectedFields = new Person$CompiledMirror(expected).fields;
  var actualFields = new Person$CompiledMirror(actual).fields;
  for (var fieldName in expectedFields.keys) {
    expect(actualFields[fieldName](), expectedFields[fieldName]());

Much simpler and much more reliable!

Other uses #

There are other uses for mirrors. If there's a use case that you'd like a compiled mirror for, please file an issue.


import 'package:compiled_mirrors/compiled_mirrors.dart';
import 'package:compiled_mirrors/equality.dart';

import 'example.compiled_mirrors.dart';

class Example {
  String foo;
  int bar;

  bool operator ==(Object other) =>
      MirrorEquality.equals(this, other, (c) => new Example$CompiledMirror(c));

  int get hashCode =>
      MirrorEquality.hash(this, (c) => new Example$CompiledMirror(c));

  String toString() =>
      MirrorEquality.asString(this, (c) => new Example$CompiledMirror(c));

Use this package as a library

1. Depend on it

Add this to your package's pubspec.yaml file:

  compiled_mirrors: ^0.1.0

2. Install it

You can install packages from the command line:

with pub:

$ pub get

Alternatively, your editor might support pub get. Check the docs for your editor to learn more.

3. Import it

Now in your Dart code, you can use:

import 'package:compiled_mirrors/compiled_mirrors.dart';
Version Uploaded Documentation Archive
0.1.0 Mar 28, 2017 Go to the documentation of compiled_mirrors 0.1.0 Download compiled_mirrors 0.1.0 archive
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