is var and is not var work with if but not while loop

[Thaina]

using System;
using System.Threading;
					
public class Program
{
	public static void Main()
	{
		while(ShouldWork() is not bool apply)
		{
			Thread.Sleep(0);
		}
		
		Console.WriteLine(apply);
	}
	
	static bool condition = true;
	static bool? ShouldWork()
	{
		if(!condition)
			return null;
		
		return true;
	}
}

This code above give error

Compilation error (line 13, col 21): The name 'apply' does not exist in the current context

https://dotnetfiddle.net/vi1hxZ

As the logic are very simple and obvious branch prediction, while condition without internal break should allow initialize variable like if

Is it possible?

[HaloFour]

Pattern variables declared within a while condition are scoped to the loop body only.

[TahirAhmadov]

I think I may have read something about it, but can't remember the details now. What was the justification for it, do you know?

[HaloFour]

See: https://github.com/dotnet/csharplang/blob/main/meetings/2016/LDM-2016-11-30.md#scope-of-while-condition-expression-variables

and: dotnet/roslyn#15529

[Thaina]

I see. Thank you for your explanation. But still is not was the opposite of the case though. It will never use in the loop and only available outside of the loop

[HaloFour]

The pattern doesn't change the scoping of the pattern variable. It is always scoped to the body of the loop. C# doesn't have any concept of "flow scoping" where the scope of the variable follows definite assignment.