ValueObject.CompareTo handles variable number of components incorrectly

[josefblaha]

I encountered something similar like in #237, but it turned out to be related to variable number of equality components. Consider the following class:

class ListLike : ValueObject
{
    string[] components;
    	
    public ListLike(params string[] components)
    {
        this.components = components;
    }

    protected override IEnumerable<object> GetEqualityComponents()
    {
        return components;
    }
}

Using CompareTo will give these results:

var a = new ListLike("one", "two");
var b = new ListLike("one", "two", "three");
	
a.CompareTo(b) // => 0
b.CompareTo(a) // throws IndexOutOfRangeException

The first call compares only prefix of the two lists. The second call fails on expectation of same number of equality components.

I wonder if there is any generic way of comparing lists of variable length. Maybe lexicographic order would work?

[vkhorikov]

Yes, you need to include the number of elements in the collection into the equality components:

private class VOWithCollection : ValueObject
{
    readonly string[] _components;

    public VOWithCollection(params string[] components)
    {
        _components = components;
    }

    protected override IEnumerable<object> GetEqualityComponents()
    {
        yield return _components.Length;
        foreach (string component in _components)
        {
            yield return component;
        }
    }
}

[josefblaha]

This indeed works. But IMHO it's not very intuitive, that you need to implement your value object this way. What do you think about using lexicographical order like this? https://github.com/josefblaha/CSharpFunctionalExtensions/commit/bff63760d594608d7cbd37f1822613f4bcffb2ad

[vkhorikov]

Yes, your idea is indeed better. It can be simplified, though: just compare the lengths of components and otherComponents before going into the for loop. The rest can be kept as-is.