根据类型返回通用字典 [英] returning generic Dictionary depending on type

问题描述

我有一个返回Dictionary的泛型函数。如果Dictionary的键是一个字符串，我想使用String.OrdinalIgnoreCase比较器。

这是我的代码：

  public static Dictionary< K，V> getDict< K，V>（）
 {
 Dictionary< K，V> aDict; 
 
 if（typeof（K）== typeof（string））
 {
 var stringDict = new Dictionary< string，V>（StringComparer.OrdinalIgnoreCase）; 
 aDict =（Dictionary< K，V>）stringDict; //错误在这里 - 无法转换。 
} 
 else aDict = new Dictionary< K，V>（）; 
 //在这里做更多的事
 return aDict; 
} 
  

但它告诉我它

不能将 Dictionary< string，V> 转换为字典< K，V> / code>。




我应该怎么做？


  var stringDict = new Dictionary< / p> 
 K，V>（
 StringComparer.OrdinalIgnoreCase as IEqualityComparer< K>）; 
  

问题在于 Dictionary< TKey，TValue> ctor期望 IEqualityComparer< T> 。 StringComparer 为您提供 IEqualityComparer - 非泛型变体。一旦你正确地转换了你的等号比较器，你应该在你的路上。

下面的测试代码块将触发预期的异常：

  var dict = getDict< string，int>（）; 
 
 dict.Add（alpha，1）; 
 dict.Add（Alpha，2）; //触发预期的重复键例外。 
  

HTH ...

I have a generic function that returns a Dictionary. If the key of the Dictionary is a string, I want to use the String.OrdinalIgnoreCase comparer.

This is my code:

    public static Dictionary<K,V> getDict<K,V>()
    {
        Dictionary<K,V> aDict;

        if(typeof(K)==typeof(string)) 
        {
            var stringDict = new Dictionary<string, V>(StringComparer.OrdinalIgnoreCase);
            aDict = (Dictionary<K,V>)stringDict;    // error here - can't convert.
        }
        else aDict = new Dictionary<K, V>();
// do more stuff here
        return aDict;
    }

However it tells me it

can't convert a Dictionary<string,V> to a Dictionary<K,V>.

How should I be doing this?

解决方案

This should work the best for you:

var stringDict = new Dictionary<K, V>(
    StringComparer.OrdinalIgnoreCase as IEqualityComparer<K>);

The problem is that the Dictionary<TKey,TValue> ctor expects an IEqualityComparer<T>. StringComparer gives you an IEqualityComparer - the non-generic variety. Once you cast your equality comparer correctly, you should be on your way.

Test code block below will trigger the expected exception:

var dict = getDict<string, int>();

dict.Add("alpha", 1);
dict.Add("Alpha", 2);  // triggers the expected duplicate key exception.

HTH...

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