使HashSet< string>不区分大小写 [英] Make HashSet<string> case-insensitive

问题描述

我有带有HashSet参数的方法。我需要在其中包含不区分大小写的内容：

I have method with HashSet parameter. And I need to do case-insensitive Contains within it:

public void DoSomething(HashSet<string> set, string item)
{
    var x = set.Contains(item);
    ... 
}

有没有办法使现有的HashSet成为例-不敏感（不要创建新的）？

Is it any way to make existing HashSet case-insensitive (do not create new one)?

我正在寻找性能最佳的解决方案。

I'm looking for solution with best perfomance.

编辑

可以多次调用包含的内容。所以IEnumerable扩展对我来说是不可接受的，因为它的性能比本地的HashSet Contains方法要低。

Contains can be called multiple times. So IEnumerable extensions are not acceptable for me due to lower perfomance than native HashSet Contains method.

解决方案

因为，对我的问题的回答是否，这是不可能的，我创建并使用了以下方法：

Since, answer to my question is NO, it is impossible, I've created and used following method:

public HashSet<string> EnsureCaseInsensitive(HashSet<string> set)
{
    return set.Comparer == StringComparer.OrdinalIgnoreCase
           ? set
           : new HashSet<string>(set, StringComparer.OrdinalIgnoreCase);
}

推荐答案

HashSet< T> 构造函数有一个重载，可让您传入自定义的 IEqualityComparer< string> 。在静态 StringComparer 类中已经为您定义了其中一些，其中一些忽略大小写。例如：

The HashSet<T> constructor has an overload that lets you pass in a custom IEqualityComparer<string>. There are a few of these defined for you already in the static StringComparer class, a few of which ignore case. For example:

var set = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
set.Add("john");
Debug.Assert(set.Contains("JohN"));

在构造 HashSet<时必须进行此更改; T> 。一旦存在，就无法更改它正在使用的 IEqualityComparer< T> 。

You'll have to make this change at the time of constructing the HashSet<T>. Once one exists, you can't change the IEqualityComparer<T> it's using.

请注意，默认情况下（如果您不将任何 IEqualityComparer< T> 传递给 HashSet< T> ; 构造函数），它使用 EqualityComparer< T>。默认。

Just so you know, by default (if you don't pass in any IEqualityComparer<T> to the HashSet<T> constructor), it uses EqualityComparer<T>.Default instead.

问题在我发布答案后似乎已经改变。如果您必须在不区分大小写的现有商品 HashSet< string> 中进行不区分大小写的查询，则必须进行线性搜索：

The question appears to have changed after I posted my answer. If you have to do a case insensitive search in an existing case sensitive HashSet<string>, you will have to do a linear search:

set.Any(s => string.Equals(s, item, StringComparison.OrdinalIgnoreCase));

无法解决这个问题。

这篇关于使HashSet< string>不区分大小写的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！