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IEqualityComparer <double> with tolerance; How to implement GetHashCode?

I implement a reusable DoubleEqualityComparer (with user tolerance: the "epsilon" constructor parameter) to facilitate the use of LINQ with double sequences. For instance:

bool myDoubleFound = doubles.Contains(myDouble, new DoubleEqualityComparer(epsilon: 0.01));

What is the correct way to implement GetHashCode? Here is the code:

   public class DoubleEqualityComparer : IEqualityComparer<double>, IEqualityComparer<double?>
    {
        private readonly double epsilon;

        public DoubleEqualityComparer(double epsilon)
        {
            if (epsilon < 0)
            {
                throw new ArgumentException("epsilon can't be negative", "epsilon");
            }

            this.epsilon = epsilon;
        }

        public bool Equals(double x, double y)
        {
            return System.Math.Abs(x - y) < this.epsilon;
        }

        public int GetHashCode(double obj)
        {
            // ?
        }
   }

PS: I can always return the same value (for example: GetHashCode (double obj) {return 0;}) to always force the Equals (double, double) method (not very strong, I know), but I remember that this solution causes problems when a comparison is used with a dictionary ...

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2 answers

, EqualityComparer - . .

, Any + :

private static bool DoublesAreNearlyEquals(double d1, double d2, double epsilon = 0.01D)
{
    return System.Math.Abs(d1 - d2) < this.epsilon;
}

private void foo()
{
    var myDoubles = Getdoubles();
    var doubleToSearch = 42D;
    var result = myDoubles.Any(d=>DoublesAreNearlyEquals(d, doubleToSearch));
}
+4

NotSupportedException GetHashCode, . IEqualityComparer LINQ , , GetHashCode . , GetHashCode. NotHashableDoubleEqualityComparer, .

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