Minimal implementation to support derived-class copy-with overriding #90

Adam-Langley · 2024-03-08T00:52:58Z

Resolves #87 and #65

Current production copy_with_generator does not honor derivation of classes annotated with CopyWith. This means that given class A (copyWith) derived by class B (also copyWith) when an instance of B is cast to A, calling 'copyWith' will return an instance of class A, losing all of the properties of B.

It's clear this can cause issues unless the developer is cognisant.
My specific use case is where copyWith is used to mutate state in Flutter Bloc applications.

When Blocs are responding to events, every event receives the current state as the bloc-declared archetype state (i.e. MyInitialState). The the event handler will cast the state to the class that it is aware of - even though it may currently be an instance of a derived type. When calling "copyWith" all derived values are lost.

Usage

After regenerating your code with this enhancement, add override capabilities to your classes like so:

// ignore_for_file: library_private_types_in_public_api
// required to expose copyWith

@CopyWith()
final class InitialState {
  final int id;
  final String name;

  const InitialState({
    required this.id, 
    required this.name,
  });

  // classes must now declare the 'copyWith' method like so
  _$InitialStateCWProxy get copyWith => _$InitialStateCWProxyImpl(this);
}

@CopyWith()
final class ErroredState extends InitialState {
  final String errorMessage;

  const ErroredState({
    required super.id, 
    required super.name,
    required this.errorMessage,
  });

  // classes must now declare the 'copyWith' method like so. Note how it declares and returns the proxy for THIS class.
  // this is now legal because the enhanced generator declares a inherited relationship between the CWProxy interfaces
  @override
  _$ErroredStateCWProxy get copyWith => _$ErroredStateCWProxyImpl(this);
}

Effect

Here is a pseudo-code usage example for the above example

InitialState state = ErroredState(id: 1, name: 'name', errorMessage: 'error message');
var newState = state.copyWith(name: 'new name');
print('new state');

// output will be 'ErroredState(id: 1, name: 'new name', errorMessage: 'error message');

Caveats

The PR is indeed a minimal implementation. Some cases not handled are:

Generated code for derived classes will still contain definitions for the supertypes members. These are now redundant, and will produce warnings that they are overrides but do not declare @OverRide. This is benign.

Add prefix with class name

…types yet.

copyWithNull

* added nullability for generic parameter constraints * added nullability check for typing nullables

* analyzer version is set to 2.0.0 * ci minor corrections * ci corrections * a possible build fix * minor ci correction * changelog * minor

* Switching to flutter_lints + null safety code cleanup * CI corrections * named constructor feature

* basic implementation * minor * prevent unnecessary copyWithNull methods generation * naming corrections * naming + ignore cast_nullable_to_non_nullable * docs + test fixes * docs * docs * release

* fix for copyWith null for a non-nullable value * version bump * minor ci correction * minor ci correction

* Updating analyser version * Release notes

* Lint correction * tests correction

* feat(settings): create settings class with default values * refactor(settings): remove default values in favor of settings from build.yaml * feat(settings): get settings from config and make available globally * refactor(settings): change type of #readClassAnnotation to `CopyWithAnnotation` to assert values * feat: create pubspec overrides to always read from project * feat(target annotation): annotate copy_with annotations with Target for better linting * style: organize code (alphabetize) * feat(positioned): add `isPositioned` property to `FieldInfo` * refactor(positioned): remove positional check and unneeded sort * feat(positioned): add check for positioned to include param name * feat: add tests for positioned fields * refactor(positioned): remove named field exceptions tests * feat(positioned): add set settings for testing * fix(positioned): tests for positioned params * feat(field): create `CopyWithFieldAnnotation` * feat(field): remove default values in favor of `CopyWithFieldAnnotation` default values * refactor(field): remove `immutable` prop and replace with `fieldAnnotation` * refactor(fields) reference new `fieldAnnotation` prop for immutable * feat(nullable): add check for null args and add ignores for file * fix: tests to include new additions * docs: update readme

* removing global Settings object + testing global settings * sort_constructors_first * tests fix * minor corrections * version bump to 5.0.0 to avoid compatibility issues * minor corrections

* Update copy_with_generator.dart * Update pubspec.yaml * remove unnecessary ignore comment. * removed unnecessary cast_nullable_to_non_nullable comment * Update pubspec.yaml * Update copy_with_generator.dart removed unnecessary ! cast * Update pubspec.yaml * Update copy_with_generator.dart ! for non nullable fields * Update pubspec.yaml * Update copy_with_generator.dart * Update pubspec.yaml * Update copy_with_generator.dart * Update pubspec.yaml

* test to cover all mentioned nullability issues * minor * minor * ci correction * use analyse action to output errors correctly to the CI dashboard actions * minor corrections * crashing dynamic test case * minor * show warnings from "dart run test" * Revert "show warnings from "dart run test"" This reverts commit f0d4ae3. * introspecting the class itself about the relevant constructors parameters * have ! only when the field of the class is non-nullable * Roll back feature with nullable field and non-nullable constructor. * tests + introducing an error when fields nullability not in sync with the constructor * remove question mark from dynamic input parameters * version bump

* Fixing use case described in numen31337#79 * version bump * test fix

* migrate to dart 3 * fix a small issue related to dart 3

Current production copy_with_generator does not honour derivation of classes annotated with CopyWith. This means that given class A (copyWith) derived by class B (also copyWith) when an instance of B is cast to A, calling 'copyWith' will return an instance of class A, losing all of the properties of B.

numen31337 and others added 30 commits December 5, 2019 19:39

copy_with_extension package

52e97a6

copy_with_extension_gen package

e91061d

copy_with_extension package corrections

4b9b96f

copy_with_extension_gen package corrections

0beeb13

adding a named parameters check

559d207

metadata fixes

d716488

code style correction

61f7b48

minor metadata corrections

d92858a

minor metadata corrections

fc9f3ab

Update copy_with_generator.dart

3c6654a

Merge pull request numen31337#1 from glaciusmss/master

01a2f53

Add prefix with class name

metadata update

746ab3f

README file update

a70c1cb

Suppresses some of the analyzer's rules as we do not support generic …

8c285b9

…types yet.

tests and dependencies correction

cc5ffc9

copyWithNull

aebd05b

Adding a simple project for the internal testing purposes

702d6c8

Merge pull request numen31337#9 from JuanM04/master

1203c12

copyWithNull

resilience for the null input in the copyWithNull function

bf8424c

introducing an option to generate a copyWithNull function

0f4480c

adding some documentation

9cc34d0

dependency update + test

41392dd

minor corrections

25490a1

minor cleanup

589ba3b

adding generics support + removing deprecated type.name API

2c8e665

metadata

e8b7d22

metadata

9714363

Update issue templates

1e84452

Delete custom.md

abf8b50

Create config.yml

f835721

josiahsrc and others added 28 commits June 24, 2021 17:18

Fix nullable generic constraint generation bug (numen31337#37)

c701325

* added nullability for generic parameter constraints * added nullability check for typing nullables

pedantic version bump + NullableGenericTestCase

a52877f

build_runner version bump

8fb1120

release 2.0.2

852254b

Analyzer version (numen31337#39)

0b685a8

* analyzer version is set to 2.0.0 * ci minor corrections * ci corrections * a possible build fix * minor ci correction * changelog * minor

Update run_tests.yml

0febc9f

Named constructor + flutter_lints + cleanup (numen31337#41)

c5d414f

* Switching to flutter_lints + null safety code cleanup * CI corrections * named constructor feature

Version 3.0 - Copy with field feature (numen31337#42)

36118fd

Version 4.0: copyWith(...) function nullability support (numen31337#43)

7907433

* basic implementation * minor * prevent unnecessary copyWithNull methods generation * naming corrections * naming + ignore cast_nullable_to_non_nullable * docs + test fixes * docs * docs * release

fix for copyWith null for a non-nullable value (numen31337#46)

274f369

* fix for copyWith null for a non-nullable value * version bump * minor ci correction * minor ci correction

typo fix

142ff3c

Updating analyser version (numen31337#53)

91c11fc

* Updating analyser version * Release notes

Lint correction (numen31337#59)

7c7b207

* Lint correction * tests correction

private extensions for private classes (numen31337#61)

5ab74df

improving documentation (numen31337#62)

585047b

version bump + changelog (numen31337#63)

ecf722e

Bumped to analyzer 5 version (numen31337#67)

cad48fb

CHANGELOG

88ab47b

Release 5.0.0 (numen31337#71)

794f49e

* removing global Settings object + testing global settings * sort_constructors_first * tests fix * minor corrections * version bump to 5.0.0 to avoid compatibility issues * minor corrections

Fixing use case described in numen31337#79 (numen31337#80)

c05d9d7

* Fixing use case described in numen31337#79 * version bump * test fix

Migrate to Dart 3 (numen31337#82)

3371159

* migrate to dart 3 * fix a small issue related to dart 3

version bump

3580988

Allow analyzer v6 (numen31337#86)

e4ef507

analyzer 6+

7b62b4a

numen31337 closed this Jul 13, 2024

numen31337 force-pushed the master branch from 7b62b4a to 310a4c7 Compare July 13, 2024 19:45

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Minimal implementation to support derived-class copy-with overriding #90

Minimal implementation to support derived-class copy-with overriding #90

Adam-Langley commented Mar 8, 2024

Minimal implementation to support derived-class copy-with overriding #90

Minimal implementation to support derived-class copy-with overriding #90

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Adam-Langley commented Mar 8, 2024

Usage

Effect

Caveats