initial

.gitignore

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+# Created by https://www.toptal.com/developers/gitignore/api/dart,visualstudiocode
+# Edit at https://www.toptal.com/developers/gitignore?templates=dart,visualstudiocode
+
+### Dart ###
+# See https://www.dartlang.org/guides/libraries/private-files
+
+# Files and directories created by pub
+.dart_tool/
+.packages
+build/
+# If you're building an application, you may want to check-in your pubspec.lock
+pubspec.lock
+
+# Directory created by dartdoc
+# If you don't generate documentation locally you can remove this line.
+doc/api/
+
+# dotenv environment variables file
+.env*
+
+# Avoid committing generated Javascript files:
+*.dart.js
+*.info.json      # Produced by the --dump-info flag.
+*.js             # When generated by dart2js. Don't specify *.js if your
+                 # project includes source files written in JavaScript.
+*.js_
+*.js.deps
+*.js.map
+
+.flutter-plugins
+.flutter-plugins-dependencies
+
+### Dart Patch ###
+# dotenv environment variables file
+.env
+
+### VisualStudioCode ###
+.vscode/*
+!.vscode/settings.json
+!.vscode/tasks.json
+!.vscode/launch.json
+!.vscode/extensions.json
+*.code-workspace
+
+# Local History for Visual Studio Code
+.history/
+
+### VisualStudioCode Patch ###
+# Ignore all local history of files
+.history
+.ionide
+
+# Support for Project snippet scope
+!.vscode/*.code-snippets
+
+# End of https://www.toptal.com/developers/gitignore/api/dart,visualstudiocode

.vscode/launch.json

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+{
+    // Use IntelliSense to learn about possible attributes.
+    // Hover to view descriptions of existing attributes.
+    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "name": "reference_wrapper",
+            "program": "example/reference_wrapper_example.dart",
+            "request": "launch",
+            "type": "dart"
+        }
+    ]
+}

CHANGELOG.md

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+## 1.0.0
+
+- Initial version of the package.

LICENSE

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+BSD 3-Clause License
+
+Copyright (c) 2021, Márton Matuz
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+1. Redistributions of source code must retain the above copyright notice, this
+   list of conditions and the following disclaimer.
+
+2. Redistributions in binary form must reproduce the above copyright notice,
+   this list of conditions and the following disclaimer in the documentation
+   and/or other materials provided with the distribution.
+
+3. Neither the name of the copyright holder nor the names of its
+   contributors may be used to endorse or promote products derived from
+   this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

README.md

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+`Reference Wrapper` is a Dart package which simulates `pass by reference` feature using Wrapper class which holds the value.
+
+# Usage
+> Use this package if you are calling a function that needs to modify its arguments
+
+## There are two ways to read / write the value
+
+```dart
+var x = Ref<num?>(null);
+var read1 = x.ref;      // first way to read
+var read2 = x();        // second way to read
+
+x.ref = 10;             // first way to write
+x(10);                  // second way to write
+```
+
+## Example
+```dart
+void twice(Ref<num> x, Ref<num> y) {
+  x.ref *= 2;
+  y.ref *= 2;
+}
+
+void test() {
+  var x = Ref<num>(5);
+  var y = Ref<num>(7);
+
+  twice(x, y);
+  print(x.ref); // 10
+  print(y.ref); // 14
+}
+```
+
+## Advanced Example
+```dart
+void twice(Ref<num> x, Ref<num> y) {
+  x(x() * 2);
+  y(y() * 2);
+}
+
+void test() {
+  var x = Ref<num>(5);
+  var y = Ref<num>(7);
+
+  twice(x, y);
+  print(x()); // 10
+  print(y()); // 14
+}
+```

analysis_options.yaml

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+# This file configures the static analysis results for your project (errors,
+# warnings, and lints).
+#
+# This enables the 'recommended' set of lints from `package:lints`.
+# This set helps identify many issues that may lead to problems when running
+# or consuming Dart code, and enforces writing Dart using a single, idiomatic
+# style and format.
+#
+# If you want a smaller set of lints you can change this to specify
+# 'package:lints/core.yaml'. These are just the most critical lints
+# (the recommended set includes the core lints).
+# The core lints are also what is used by pub.dev for scoring packages.
+
+include: package:lints/recommended.yaml
+
+# Uncomment the following section to specify additional rules.
+
+# linter:
+#   rules:
+#     - camel_case_types
+
+# analyzer:
+#   exclude:
+#     - path/to/excluded/files/**
+
+# For more information about the core and recommended set of lints, see
+# https://dart.dev/go/core-lints
+
+# For additional information about configuring this file, see
+# https://dart.dev/guides/language/analysis-options

example/reference_wrapper_example.dart

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+import 'package:reference_wrapper/reference_wrapper.dart';
+
+void twice(Ref<num> x, Ref<num> y) {
+  x.ref *= 2;
+  y.ref *= 2;
+}
+
+void twiceAdvanced(Ref<num> x, Ref<num> y) {
+  x(x() * 2);
+  y(y() * 2);
+}
+
+void main() {
+  var x = Ref<num>(5);
+  var y = Ref<num>(7);
+
+  twice(x, y);
+  print(x.ref); // 10
+  print(y.ref); // 14
+
+  twiceAdvanced(x, y);
+  print(x()); // 20
+  print(y()); // 28
+}

lib/reference_wrapper.dart

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+library reference_wrapper;
+
+export 'src/reference_wrapper.dart';

lib/src/reference_wrapper.dart

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+/// Wraps an arbitary object, if caller method pass [Ref] to callee method, then
+/// any changes made on [Ref.ref] will affect caller too.
+///
+/// There are two ways to read / write the value:
+///
+/// ```dart
+/// var x = Ref<num?>(null);
+/// x.ref;      // first way to read
+/// x();        // second way to read
+///
+/// x.ref = 10; // first way to write
+/// x(15);      // second way to write
+/// ```
+///
+/// **Example:**
+/// ```dart
+/// void twice(Ref<num> x, Ref<num> y) {
+///   x.ref *= 2;
+///   y.ref *= 2;
+/// }
+///
+/// void test() {
+///   var x = Ref<num>(5);
+///   var y = Ref<num>(7);
+///
+///   twice(x, y);
+///   print(x.ref); // 10
+///   print(y.ref); // 14
+/// }
+/// ```
+///
+/// **Advanced Example:**
+/// ```dart
+/// void twiceAdvanced(Ref<num> x, Ref<num> y) {
+///   x(x() * 2);
+///   y(y() * 2);
+/// }
+///
+/// void test() {
+///   var x = Ref<num>(5);
+///   var y = Ref<num>(7);
+///
+///   twiceAdvanced(x, y);
+///   print(x()); // 10
+///   print(y()); // 14
+/// }
+/// ```
+abstract class Ref<T> {
+  Ref._();
+
+  factory Ref(T ref) = _Ref;
+
+  T get ref;
+
+  set ref(T ref);
+
+  T call([T ref]);
+
+  Type get genericRuntimeType;
+
+  static Type genericStaticType<S>(Ref<S> ref) => S;
+
+  @override
+  String toString() => 'Ref(ref: $ref)';
+}
+
+class _Undefined {}
+
+class _Ref<T> extends Ref<T> {
+  @override
+  T ref;
+
+  _Ref(this.ref) : super._();
+
+  @override
+  T call([Object? ref = _Undefined]) {
+    return identical(ref, _Undefined) ? this.ref : this.ref = ref as T;
+  }
+
+  @override
+  Type get genericRuntimeType => T;
+
+  @override
+  bool operator ==(Object other) {
+    if (identical(this, other)) {
+      return true;
+    }
+
+    return other is _Ref<T> &&
+        other.genericRuntimeType == genericRuntimeType &&
+        other.ref == ref;
+  }
+
+  @override
+  int get hashCode => ref.hashCode;
+}

pubspec.yaml

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+name: reference_wrapper
+description: A Dart package which simulates pass by reference feature.
+version: 1.0.0
+repository: https://github.com/maRci002/reference_wrapper
+homepage: https://github.com/maRci002/reference_wrapper
+
+environment:
+  sdk: '>=2.12.0 <3.0.0'
+
+dev_dependencies:
+  lints: ^1.0.0
+  test: ^1.16.0