创建一个通用方法来使用我为特定类型定义的 EqualityComparer答案

【问题标题】：Create a generic method to use EqualityComparer that I have defined for specific types创建一个通用方法来使用我为特定类型定义的 EqualityComparer
【发布时间】：2020-08-19 08:32:41
【问题描述】：

我有很多对象，我想检查这些对象的列表是否相等。

我为每个对象定义了一个 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();
}

然后我想调用以下方法来检查 BaseAssociatedEntity 类型的 2 个列表是否为 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;
}

但我最终为我拥有的每个对象编写了这个 BothNullOrEqual 方法：

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;
}

等等..如何使用我专门定义的 EqualityComparer 使这个方法通用，以便它适用于所有类型？

【问题讨论】：

标签： c# generics collections equality iequalitycomparer

【解决方案1】：

只需使方法在数据类型和比较器类型中都通用：

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());
}

另一种单一表达式版本：

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());

【讨论】：