How to use the IEqualityComparer

Question

I have some bells in my database with the same number. I want to get all of them without duplication. I created a compare class to do this work, but the execution of the fun

Answer 1

If you want a generic solution without boxing:

public class KeyBasedEqualityComparer : IEqualityComparer
{
    private readonly Func _keyGetter;

    public KeyBasedEqualityComparer(Func keyGetter)
    {
        _keyGetter = keyGetter;
    }

    public bool Equals(T x, T y)
    {
        return EqualityComparer.Default.Equals(_keyGetter(x), _keyGetter(y));
    }

    public int GetHashCode(T obj)
    {
        TKey key = _keyGetter(obj);

        return key == null ? 0 : key.GetHashCode();
    }
}

public static class KeyBasedEqualityComparer
{
    public static KeyBasedEqualityComparer Create(Func keyGetter)
    {
        return new KeyBasedEqualityComparer(keyGetter);
    }
}

usage:

KeyBasedEqualityComparer.Create(x => x.Numf)