Dictionary key not working as a type of Tuple

Question

I have a situation where I would need a dictionary with this type of key, but it doesn't seem to find the equivalent key later on.

Dictionary<Tuple<int[], int>, object> cache = new Dictionary<Tuple<int[], int>, object>();

cache.Add(Tuple.Create(new int[]{1}, 1), new object());

Assert.That(cache.ContainsKey(Tuple.Create(new int[] { 1 }, 1))); // This fails

I've tested it by using a Tuple<int, int> and it seems to be working fine, but in my case I really need some sort of Tuple<int[], int> and with that type of key, it doesn't work.

Is there any other alternative to this that would be working?

The problem is that I can't lookup in my dicco with that type of tuple — Samuel Poirier, Mar 28 '14 at 19:45
well that's because you can't compare arrays that way as seen [here](http://stackoverflow.com/questions/4423318/how-to-compare-arrays-in-c) — Jonesopolis, Mar 28 '14 at 19:46

score 9 · Accepted Answer · answered Mar 28 '14 at 19:46

Arrays are not comparable. For example:

var array1 = new int[] { 1 };
var array2 = new int[] { 1 };
Debug.WriteLine(array1 == array2); // this returns false
Debug.WriteLine(Object.Equals(array1, array2)) // this returns false

You need to do one of two things:

1) Replace int[] with a custom class that implements the necessary Equals and GetHashCode overrides.

2) Write a class that implements IEqualityComparer<Tuple<int[], int>>. That class will provide the Equals and GetHashCode methods for Tuple<int[], int>s. Provide an instance of that class to your Dictionary<Tuple<int[], int>, object>

score 0 · Answer 2 · edited May 23 '17 at 12:05

You can not compare array with == You can use this code:

 static bool ArraysEqual<T>(T[] array1, T[] array2)
    {
        if (ReferenceEquals(array1,array2))
            return true;

        if (array1 == null || array2 == null)
            return false;

        if (array1.Length != array2.Length)
            return false;

        EqualityComparer<T> comparer = EqualityComparer<T>.Default;
        for (int i = 0; i < array1.Length; i++)
        {
            if (!comparer.Equals(array1[i], array2[i])) return false;
        }
        return true;
    }

Dictionary key not working as a type of Tuple

2 Answers2