Create a generic method to use EqualityComparer that I have defined for specific types

Question

I have many objects in which I want to check that lists of those objects are equal.

For each object I have defined an EqualityComparer:

public class BaseAssociatedEntity : BasePage
{
    protected IWebElement EntityElement;
    protected virtual IWebElement EntityLink => EntityElement.FindElement(By.TagName("a"));
    public string EntityName => EntityLink.Text;

    public BaseAssociatedEntity(IWebElement entityElement, IWebDriver driver, string username, string password) 
        : base(driver, driver.Url, username, password, TimeoutInSecondsConstants.Three)
    {
        EntityElement = entityElement;
    }

    public bool Equals(BaseAssociatedEntity that)
    {
        return EntityName == that.EntityName;
    }
}

public class BaseAssociatedEntityEqual : EqualityComparer<BaseAssociatedEntity>
{
    public override bool Equals(BaseAssociatedEntity x, BaseAssociatedEntity y)
    {
        if (ReferenceEquals(x, y)) return true;
        if (x is null || y is null) return false;

        return x.Equals(y);
    }

    public override int GetHashCode(BaseAssociatedEntity obj) => obj.GetHashCode();
}

I then want to call the following method to check that 2 lists of type BaseAssociatedEntity are SequenceEqual():

protected bool BothNullOrEqual(List<BaseAssociatedEntity> left, List<BaseAssociatedEntity> right)
{
    if (left == null && right == null) return true;
    if (left != null && right != null) return left.SequenceEqual(right, new BaseAssociatedEntityEqual());
    return false;
}

But I end up writing this BothNullOrEqual method for every single object that I have:

protected bool BothNullOrEqual(List<NotificationGroupAssociatedEntity> left,
    List<NotificationGroupAssociatedEntity> right)
{
    if (left == null && right == null) return true;
    if (left != null && right != null) return left.SequenceEqual(right, new NotificationGroupAssociatedEntityEqual());
    return false;
}

And so on.. How can I make this method generic so that it works for all types, using the EqualityComparer that I have specifically defined?

score 2 · Accepted Answer · answered Aug 19 '20 at 08:36

Just make the method generic in both the data type and the comparer type:

public static bool BothNullOrEqual<TData, TEqualityComparer>
    (IEnumerable<TData> left, IEnumerable<TData> right)
    where TEqualityComparer : IEqualityComparer<TData>, new()
{
    if (left is null && right is null)
    {
        return true;
    }
    if (left is null || right is null)
    {
        return false;
    }
    return left.SequenceEqual(right, new TEqualityComparer());
}

An alternative single expression version:

public static bool BothNullOrEqual<TData, TEqualityComparer>
    (IEnumerable<TData> left, IEnumerable<TData> right)
    where TEqualityComparer : IEqualityComparer<TData>, new() =>
    left is null
    ? right is null
    : right is object && left.SequenceEqual(right, new TEqualityComparer());

Create a generic method to use EqualityComparer that I have defined for specific types

1 Answers1