using System;

using System.Collections.Generic;

public class Program

{

    private static Length _bar;

    public static void Main()

    {

        // Error: cannot convert from QuantityEqualityComparer to IEqualityComparer<Length>

        Set(ref _bar, new Length(), new QuantityEqualityComparer());

    }

    // from Mvvm

    public static bool Set<T>(ref T field, T value, IEqualityComparer<T> comparer)

    {

        return true;

    }

}

public class QuantityEqualityComparer : IEqualityComparer<IQuantity>

{

    public bool Equals(IQuantity x, IQuantity y)

    {

        return true;

    }

    public int GetHashCode(IQuantity obj)

    {

        return 0;

    }

}

​

// from UnitsNet

public interface IQuantity

{

}

​

public struct Length : IQuantity, IEquatable<Length>

{

    public bool Equals(Length other)

    {

        return true;

    }

}