Coding Lifestyle

Dictionary Extensions: Define useful extensions to play safe January 18, 2012

   if (searchCriteria.ContainsKey(key) &&
       !string.IsNullOrEmpty(searchCriteria[key]))
       searchTerm = searchCriteria[key];

Ever have a dictionary or similar data structure and your code has many repeated checks to pull the value when in reality you’d be happy with a default value like null or string.Empty? Well, consider the following extension to Dictionary:

    public static class DictionaryExtensions
    {
        public static TValue GetSafeValue<TKey, TValue>(this Dictionary<TKey, TValue> dictionary, TKey key)
        {
            TValue result = default(TValue);
            dictionary.TryGetValue(index, out result);
            return result;
        }
    }

Let’s you do:

    Dictionary bob = new Dictionary();
    string safe = bob.GetSafeValue(100);
    System.Diagnostics.Trace.WriteLine(safe);

where safe defaults to “” as it hasn’t been added. Stop! I know what you’re going to say and I thought of that too. You can control the default value as well:

    public static class DictionaryExtensions
    {
        /// <summary>
        /// Gets the safe value associated with the specified key.
        /// </summary>
        /// <typeparam name="TKey">The type of the key.</typeparam>
        /// <typeparam name="TValue">The type of the value.</typeparam>
        /// <param name="dictionary">The dictionary.</param>
        /// <param name="key">The key of the value to get.</param>
        public static TValue GetSafeValue<TKey, TValue>(this Dictionary<TKey, TValue> dictionary, TKey key)
        {
            return dictionary.GetSafeValue(key, default(TValue));
        }

        /// <summary>
        /// Gets the safe value associated with the specified key.
        /// </summary>
        /// <typeparam name="TKey">The type of the key.</typeparam>
        /// <typeparam name="TValue">The type of the value.</typeparam>
        /// <param name="dictionary">The dictionary.</param>
        /// <param name="key">The key of the value to get.</param>
        /// <param name="defaultValue">The default value.</param>
        public static TValue GetSafeValue<TKey, TValue>(this Dictionary<TKey, TValue> dictionary, TKey key, TValue defaultValue)
        {
            TValue result;
            if (key == null || !dictionary.TryGetValue(key, out result))
                result = defaultValue;
            return result;
        }
    }

Let’s you do:

   Dictionary bob = new Dictionary();
   string safe = bob.GetSafeValue(100, null);
   System.Diagnostics.Trace.WriteLine(safe);

where safe is null.

There’s obviously something wrong with me because I still think this stuff is cool.

I’m developing a nice little set of extensions at this point.  Often it seems like overkill to encapsulate handy functions like these in a class. I had started by deriving a class from Dictionary<TKey, TValue> but changed over to the above.