Dictionary Extensions: Define Useful Extensions to Play Safe

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 say 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 say 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.