在 StringComparison 和 StringComparer 之间转换的优雅方式？

Question

一些 .NET 方法使用 StringComparison as parameter, some use StringComparer (often in form of IComparer)。区别很明显。是否有一些优雅的方法如何从 StringComparer 获取 StringComparison 或者反之亦然？

我总是可以编写使用 Case 语句的简单方法，但也许 .NET 中已经存在一些我忽略的东西。

Answer 1

没有开箱即用的东西，但您可以自己在比较器和比较器之间创建一个简单的映射：

Dictionary<StringComparison, StringComparer> comparsionToComparer = 
                        new Dictionary<StringComparison, System.StringComparer>
{
    { StringComparison.CurrentCulture, StringComparer.CurrentCulture },
    { StringComparison.CurrentCultureIgnoreCase, StringComparer.CurrentCultureIgnoreCase },
    { StringComparison.InvariantCulture, StringComparer.InvariantCulture },
    { StringComparison.InvariantCultureIgnoreCase, StringComparer.InvariantCultureIgnoreCase },
    { StringComparison.Ordinal, StringComparer.Ordinal },
    { StringComparison.OrdinalIgnoreCase, StringComparer.OrdinalIgnoreCase }
}

当您需要合适的比较器时：

var invariantComparer = comparsionToComparer[StringComparsion.InvariantCulture];

编辑：

使用 C#-6 字典初始化程序语法：

Dictionary<StringComparison, StringComparer> comparsionToComparer = 
                            new Dictionary<StringComparison, System.StringComparer>
{
    [StringComparison.CurrentCulture] = StringComparer.CurrentCulture,
    [StringComparison.CurrentCultureIgnoreCase] = StringComparer.CurrentCultureIgnoreCase,
    [StringComparison.InvariantCulture] = StringComparer.InvariantCulture,
    [StringComparison.InvariantCultureIgnoreCase] = StringComparer.InvariantCultureIgnoreCase,
    [StringComparison.Ordinal] = StringComparer.Ordinal,
    [StringComparison.OrdinalIgnoreCase] = StringComparer.OrdinalIgnoreCase
};

此外，指的是线程当前文化的问题，我已将其丢弃，应该予以考虑

Answer 2

从 StringComparison 到 StringComparer 很简单 - 只需创建一个 Dictionary<StringComparison, StringComparer>:

var map = new Dictionary<StringComparison, StringComparer>
{
    { StringComparison.Ordinal, StringComparer.Ordinal },
    // etc
};

每个 StringComparison 值都有一个 StringComparer，所以这种方法很容易工作。请注意，StringComparer.CurrentCulture 取决于当前的线程文化 - 因此，如果您填充字典然后修改线程的文化（或者从具有不同文化的不同线程进行修改），您可能会得到错误的值。您可能想要 Dictionary<StringComparison, Func<StringComparer>>:

var map = new Dictionary<StringComparison, Func<StringComparer>>
{
    { StringComparison.Ordinal, () => StringComparer.Ordinal },
    // etc
};

然后你可以通过调用委托随时得到一个比较器：

var comparer = map[comparison]();

走另一条路是行不通的，因为不是每个StringComparer都有合适的StringComparison。例如，假设我（在英国）为法语创建了一个 StringComparer（StringComparer.Create(new CultureInfo(..., true))。那代表哪个 StringComparison？这对当前文化、不变文化或序数不正确比较。

Answer 3

vb.net 版本基于已接受的答案（和 Option Infer Off）：

Dim map As New Dictionary(Of StringComparison, Func(Of StringComparer))() _
    From {
        {StringComparison.CurrentCulture, Function() StringComparer.CurrentCulture},
        {StringComparison.CurrentCultureIgnoreCase, Function() StringComparer.CurrentCultureIgnoreCase},
        {StringComparison.InvariantCulture, Function() StringComparer.InvariantCulture},
        {StringComparison.InvariantCultureIgnoreCase, Function() StringComparer.InvariantCultureIgnoreCase},
        {StringComparison.Ordinal, Function() StringComparer.Ordinal},
        {StringComparison.OrdinalIgnoreCase, Function() StringComparer.OrdinalIgnoreCase}
    }

用法：

Dim comparer As StringComparer = map(comparison)()

Answer 4

一个完整的扩展方法，适合任何需要快速复制+粘贴的人：

public static class StringComparisonExtensions
{
  // from 
  private static readonly Dictionary<StringComparison, Func<StringComparer>> ComparsionToComparer =
    new Dictionary<StringComparison, Func<StringComparer>>
      {
        [StringComparison.CurrentCulture] = () => StringComparer.CurrentCulture,
        [StringComparison.CurrentCultureIgnoreCase] = () => StringComparer.CurrentCultureIgnoreCase,
        [StringComparison.InvariantCulture] = () => StringComparer.InvariantCulture,
        [StringComparison.InvariantCultureIgnoreCase] = () => StringComparer.InvariantCultureIgnoreCase,
        [StringComparison.Ordinal] = () => StringComparer.Ordinal,
        [StringComparison.OrdinalIgnoreCase] = () => StringComparer.OrdinalIgnoreCase
      };

  /// <summary>
  ///  Retrieves a string comparer for the given StringComparison.
  /// </summary>
  public static StringComparer ToComparer(this StringComparison comparison)
  {
    return ComparsionToComparer.GetValueOrDefault(comparison)?.Invoke();
  }
}

Answer 5

    public static StringComparer ToComparer(this StringComparison comparison)
    {
        switch (comparison) {
            case StringComparison.CurrentCulture:
                return StringComparer.CurrentCulture;
            case StringComparison.CurrentCultureIgnoreCase:
                return StringComparer.CurrentCultureIgnoreCase;
            case StringComparison.InvariantCulture:
                return StringComparer.InvariantCulture;
            case StringComparison.InvariantCultureIgnoreCase:
                return StringComparer.InvariantCultureIgnoreCase;
            case StringComparison.Ordinal:
                return StringComparer.Ordinal;
            case StringComparison.OrdinalIgnoreCase:
                return StringComparer.OrdinalIgnoreCase;
            default:
                break;
        }

        throw new NotImplementedException("Unknown StringComparison");
    }

在 StringComparison 和 StringComparer 之间转换的优雅方式？

Elegant way of converting between StringComparison and StringComparer?

.net

string

string-comparison