[GitHub] [royale-compiler] joshtynjala opened a new issue #82: Private constructors in ActionScript

[GitBox <gi...@apache.org>]

joshtynjala opened a new issue #82: Private constructors in ActionScript
URL: https://github.com/apache/royale-compiler/issues/82
 
 
   ## Proposed syntax
   
   For singletons:
   
   ``` actionscript
   package com.example
   {
   	public class MySingletonClass
   	{
   		private static var _instance:MySingletonClass;
   
   		public static function get instance():MySingletonClass
   		{
   			if(!_instance)
   			{
   				_instance = new MySingletonClass();
   			}
   			return _instance;
   		}
   
   		private function MySingletonClass()
   		{
   			
   		}
   	}
   }
   ```
   
   Also useful for classes that are meant to provide static methods only:
   
   ``` actionscript
   package com.example
   {
   	public class MyUtils
   	{
   		public static function utilityFunction1():void {}
   		public static function utilityFunction2():void {}
   		public static function utilityFunction3():void {}
   
   		private function MyUtils() {}
   	}
   }
   ```
   
   ## Semantics
   
   At compile time, use of a class with a private constructor in a `new` statement should result in an error, if it is in another class.
   
   ``` actionscript
   new MySingletonClass(); //error in another class
   ```
   
   Similar to the `InaccessibleMethodReferenceProblem` that is created when trying to call a method in the wrong scope, there should be a new problem for private constructors with this message:
   
   > Attempted access of inaccessible constructor through a reference with static type MySingletonClass
   
   When this feature is enabled, an alternative to `ConstructorMustBePublicProblem` should be mention `private` too:
   
   > A constructor can only be declared public or private
   
   ## How to enable
   
   New ActionScript syntax should be opt-in because IDEs and other tooling may use the Apache Royale compiler with other SDKs that don't support the syntax. Developers can enable private constructors using a new `allow-private-constructors` compiler option.
   
   ``` sh
   mxmlc -allow-private-constructors App.mxml
   ```

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