自定义“ToString()”实现提供程序的通用 .NET 接口？

Question

我为一些单元测试编写了一个辅助方法，以使用自定义 IEqualityComparer<T> 实现来断言“集合等价”：

/// <summary>
/// Known issue: this checks for set-equality, which means that duplicate items will be interpreted as one.
/// </summary>
public static void AssertCollectionsAreEquivalent<T>(ICollection<T> expected, ICollection<T> actual,
        IEqualityComparer<T> comparer)
{
    T[] commonMembers = expected.Intersect(actual, comparer).ToArray();
    T[] missingMembers = expected.Except(actual, comparer).ToArray();
    T[] extraMembers = actual.Except(expected, comparer).ToArray();
    if (missingMembers.Any() || extraMembers.Any())
    {
        Assert.Fail("Collections were not equivalent.{0}Common members: {1}{0}Missing members: {2}{0}Extra members: {3}",
            Environment.NewLine,
            string.Join(", ", commonMembers.Select(t => t.ToString())),
            string.Join(", ", missingMembers.Select(t => t.ToString())),
            string.Join(", ", extraMembers.Select(t => t.ToString())));
    }
}

在此过程中，允许调用者提供可以提供自定义字符串格式的对象似乎很有帮助，但我没有看到 .NET 中符合要求的接口。我最终暂时使用了Func<T, string>：

/// <summary>
/// Known issue: this checks for set-equality, which means that duplicate items will be interpreted as one.
/// </summary>
private static void AssertCollectionsAreEquivalent<T>(ICollection<T> expected, ICollection<T> actual,
    IEqualityComparer<T> comparer, Func<T, string> toStringConverter)
{
    T[] commonMembers = expected.Intersect(actual, comparer).ToArray();
    T[] missingMembers = expected.Except(actual, comparer).ToArray();
    T[] extraMembers = actual.Except(expected, comparer).ToArray();
    if (missingMembers.Any() || extraMembers.Any())
    {
        Assert.Fail("Collections were not equivalent.{0}Common members: {1}{0}Missing members: {2}{0}Extra members: {3}",
            Environment.NewLine,
            string.Join(", ", commonMembers.Select(toStringConverter)),
            string.Join(", ", missingMembers.Select(toStringConverter)),
            string.Join(", ", extraMembers.Select(toStringConverter)));
    }
}

这样做的动机是一个单元测试套件，它使用一个通用的测试 DTO 从数据存储中检索项目，但我们对不同的测试场景有不同的相等定义（因此IEqualityComparer<T> 参数）。我知道我可以定义一个自定义界面来做我想做的事：

public interface IToStringProvider<in T>
{
    string ToString(T obj);
}

...但我希望可能有一些现有的项目可以满足要求。

Answer 1

看看IFormattable。它可能会做你想做的事，尽管方式不尽相同。您可能需要在该方法上添加类型约束，但您会发现很多类型已经实现了这一点。