I'm implementing a reusable DoubleEqualityComparer (with a custom tolerance: the "epsilon" constructor parameter) to ease the usage of LINQ with sequences of double. For example:
bool myDoubleFound = doubles.Contains(myDouble, new DoubleEqualityComparer(epsilon: 0.01));
What is the right way to implement GetHashCode? Here's 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 (ex: GetHashCode(double obj){ return 0; }) to always force the call to Equals(double, double) method (not very performant, I know), but I remember that this solution causes problems when the comparer is used with a dictionary...
I'm not sure using IEqualityComparer<T>
is the way to go. Because compared objects are not equals.
Maybe you should consider using a simple Any
clause + an utility method :
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));
}