Error in Anonymous Method contained variable

Question

I have the following method. When the Writeline Methods are calling, missing results arise. The result of the second Writeline must true otherwise, it is false, could you please advise me?

    public static void IsGreater()
    {
       var biggerThanNumber = new Predicate<int>[10];
       for (int index = 0; index < biggerThanNumber.Length; ++index)
       {
         biggerThanNumber[index] = value => value > index; 
       }
       Console.WriteLine(biggerThanNumber[5](20)); //True
       Console.WriteLine(biggerThanNumber[5](6));  //False
    }

It is unclear what your problem is. Please provide: The input. The expected output. The real output. — Christopher, Jun 06 '20 at 15:29
@Christopher OP problem is seems to be clear, because lambda expression captures loop variable — Pavel Anikhouski, Jun 06 '20 at 15:37

score 1 · Accepted Answer · answered Jun 06 '20 at 15:29

Change the method to copy loop variable into a local reference to avoid lambda closure issue in a loop. In your method value of index is always 10 hence second the console is returning false. For more info check this post

    public static void IsGreater()
    {
        var biggerThanNumber = new Predicate<int>[10];
        for (int index = 0; index < biggerThanNumber.Length; ++index)
        {
            int localCopy = index;
            biggerThanNumber[index] = value => value > localCopy;
        }
        Console.WriteLine(biggerThanNumber[5](20)); //True
        Console.WriteLine(biggerThanNumber[5](6));  //True
    }

Error in Anonymous Method contained variable

1 Answers1