C#字典扩展方法语法

public static class DictionaryExtensions
{
    public static void NewMethod(this Dictionary<TKey, TValue> dictionary, parameters)
    {
        // 扩展方法的实现逻辑
    }
}

public static class DictionaryExtensions
{
    public static TValue GetValueOrDefault<TKey, TValue>(this Dictionary<TKey, TValue> dictionary, TKey key, TValue defaultValue)
    {
        TValue value;
        if (dictionary.TryGetValue(key, out value))
        {
            return value;
        }
        return defaultValue;
    }
}

Dictionary<string, int> dictionary = new Dictionary<string, int>();
dictionary.Add("A", 1);
dictionary.Add("B", 2);

int valueA = dictionary.GetValueOrDefault("A", 0); // 返回1
int valueC = dictionary.GetValueOrDefault("C", 0); // 返回0