false negative on uninitialized reference (null pointer exception) in class method #41446

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1. Ryan Cavanaugh (RyanCavanaugh)

   added

   Design LimitationConstraints of the existing architecture prevent this from being fixedConstraints of the existing architecture prevent this from being fixed

   on Nov 9, 2020
2. RyanCavanaugh commented on Nov 9, 2020

   

   Ryan Cavanaugh (RyanCavanaugh)

   on Nov 9, 2020

   Member

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   This doesn't really tell us much, especially in the presence of virtual methods (which is going to be very common). Inlining one level instead of zero levels just creates "TypeScript isn't consistent about X" bugs.
3. beauxq commented on Nov 9, 2020

   

   Doug Hoskisson (beauxq)

   on Nov 9, 2020

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   It does not create "TypeScript isn't consistent about X" bugs.
   All of those bugs are already here. It is already inconsistent about finding some "used before being assigned" bugs and not others.
   If consistency is what you want, then you need to make it so you don't find any "used before being assigned" bugs.

   It would not create any inconsistency. It would find more bugs.
4. Ryan Cavanaugh (RyanCavanaugh)

   closed this as completedon Jun 1, 2021
5. theonlypwner commented on Apr 17, 2023

   

   Victor (theonlypwner)

   on Apr 17, 2023

   Last edited by theonlypwner

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   Doug Hoskisson (@beauxq) I noticed a similar issue that has a false negative. How can we handle something like this?

   Playground: https://www.typescriptlang.org/play?#code/JYOwLgpgTgZghgYwgAgJICFkG9kFsJgAWA9gCYAUAlAFzIBuxwpyAvgFBsIA2cAzr8gCCyYLgAOXCPnACM2NskXIARsgC8yEBADuydOSLBelBUvxEyVbMkO8AdMrvmSFSqzbtOPfnpHjJ0mCymFimigjEILxgUACuCGDEUOTKtBhuoUpZKk4ELlYA9AXICFB8hBACsSCSPhG4gRDMxLFgYe5ZzpYZJZG8xJJ2XMQA5uQADG7snlq6glS5Fq5sQA

   interface IB { method(): void }
   
   class A implements IB {
       b = new B(this)
       method() { this.b.method() } // delegation pattern
   }
   
   class B implements IB {
       constructor(b: IB) {
           b.method() // crashes unless commented out
       }
       method() { console.log(0) }
   }
   
   new A().method()

   this.b is not yet assigned when A.method is called during the construction of A, but after it is constructed, subsequent calls to A.method are perfectly fine.

   Here's a Java version of same thing (results in NullPointerException):

   public class Main {
   	interface IB { void method(); }
   
   	static class A implements IB {
   		final B b = new B(this);
   		public void method() { this.b.method(); }
   	}
   
   	static class B implements IB {
   		public B(IB b) { b.method(); }
   		public void method() { System.out.println(0); }
   	}
   
   	public static void main(String []args){
   		new A(); // crashes
   	}
   }