静态非泛型类中的泛型函数？

Question

I have a static class "Extras" in my project that I use to put methods that don't belong in any other class, such as converters. I want to add a function called DictionaryFromArrays() that I use to create a Dictionary based on an two arrays passed as parameters: one filled with keys, and another filled with values. However, I'm new to generics, and using

public static Dictionary<T, U> DictionaryFromArrays(T[] keys, U[] values)

clearly doesn't work.

I know that this is obviously not the correct way to use generics, but how would one create a function that has that effect?

Answer 1

您应该为方法声明通用类型（ DictionaryFromArrays<T, U> ）：

public static Dictionary<T, U> DictionaryFromArrays<T, U>(T[] keys, U[] values)

Answer 2

You can do it like this:

public static Dictionary<T, U> DictionaryFromArrays<T,U>(T[] keys, U[] values)
{
     var dictionary = new Dictionary<T, U>();
     if (keys.Length == values.Length)
     {
         for (int i = 0; i < keys.Length; i++)
         {
             dictionary.Add(keys[i], values[i]);
         }
     }
     else
     {
         /* throw exception */
     }

     return dictionary;
}

Answer 3

You are almost there:

 public static Dictionary<T, U> DictionaryFromArrays<T,U>(T[] keys, U[] values) 
 {return ....;}

You need to specify types in the signature, not just in arguments/return value.

Note: this pattern is heavily used in LINQ's Enumerable - static extension methods in static non-generic class.

Answer 4

The generic type was missing: <TKey, TValue> before the round brackets of the method.

Here is a possible implementation which should work:

public static Dictionary<K, V> DictionaryFromArrays<K, V>(K[] keys, V[] values, bool skipDuplicates)
{
    if (keys == null) throw new ArgumentNullException("keys");
    if (values == null) throw new ArgumentNullException("values");
    if(keys.Length != values.Length) throw new ArgumentException("Keys and Values must have the same length!");

    if (!skipDuplicates)
        return keys.Zip(values, (k, v) => new KeyValuePair<K, V>(k, v))
            .ToDictionary(kv => kv.Key, kv => kv.Value);
    else
    {
        Dictionary<K, V> dict = new Dictionary<K,V>();
        for (int i = 0; i < keys.Length; i++)
        {
            K key = keys[i];
            if (!dict.ContainsKey(key))
                dict.Add(key, values[i]);
        }
        return dict;
    }
}

Answer 5

You can use LINQ Select with index version.

public static Dictionary<T, U> DictionaryFromArrays<T,U>(T[] keys, U[] values)
{
    return keys
      .Select((k, idx) => new {key = k, value = values[idx]})
      .ToDictionary(x => key, y => value);
}