const/final lists in Java, JavaScript and TypeScript

[mittelmark]

Hello,

if I create a List with () - it becomes const/final in Java, JavaScript and Typescript. Here an example:

public static class Test3 {
	public static List<int>() GetValues (int x) {
		List<int>() y ;
		for (int i = 0; i < x; i++) {
			y.Add(i);
		}
		return(y);
		
	}
	public static void Run (string[] args)
	{
		List<int>() x; // declared const in JavaScript/TypeScript and final in Java
		List<int>() y; // declared const in JavaScript/TypeScript and final in Java
		x.Add(1); // works on C, C++, C#, D, Java, JavaScript, TypeScript, Python
		Console.WriteLine($"List x has {x.Count} elements!");		
		y = GetValues(5); // works: C, C++, C#, D, Python - fail: Java, Javascript and Typescript as y ist final/const
		Console.WriteLine($"List y has {y.Count} elements!");
	}
	public static int Main (string[] args)
	{
		Test3.Run(args); 
		return(0);
	}
}

Is this the expected behavior? Or should I replace the line with the y-initialization as:

List<int> y = GetValues(5);

[pfusik]

This is by design. List<int>() y; creates an empty list. Reassigning it later means this empty list was created for no reason - fut should report an error for this assignment.

Here are your alternatives:

a. Instead of returning a new list by value, pass an existing list by a read-write reference and add to it:

public static class Issue232A
{
    public static void GetValues(List<int>! result, int n)
    {
        for (int i = 0; i < n; i++)
            result.Add(i);
    }

    public static void Run(string[] args)
    {
        List<int>() y;
        GetValues(y, 5);
    }
}

b. Instead of creating an empty list, initialize the variable with the list returned by the method:

public static class Issue232B
{
    public static List<int>() GetValues(int n)
    {
        List<int>() y;
        for (int i = 0; i < n; i++)
            y.Add(i);
        return y;
    }

    public static void Run(string[] args)
    {
        List<int>() y = GetValues(5);
    }
}

c. Create the variable as "uninitialized storage". The syntax for this is = null, although it isn't a null reference. This is for object storage that will be assigned later.

public static class Issue232C
{
    public static List<int>() GetValues(int n)
    {
        List<int>() y;
        for (int i = 0; i < n; i++)
            y.Add(i);
        return y;
    }

    public static void Run(string[] args)
    {
        List<int>() y = null;
        y = GetValues(5);
    }
}

[mittelmark]

Ok, I understand. I should add a few more example to my tutorial. Thanks for the clarification.