/// <summary>
/// Adds a key/value pair to the <see cref="IDictionary{TKey,TValue}" /> if the key does not already
/// exist, or updates a key/value pair in the <see cref="IDictionary{TKey,TValue}" /> if the key
/// already exists. The default value will be used if key is missed to the <see cref="IDictionary{TKey,TValue}" />.
/// </summary>
/// <typeparam name="TKey">Key type.</typeparam>
/// <typeparam name="TValue">Value type.</typeparam>
/// <param name="target">Target dictionary.</param>
/// <param name="key">The key to be added or whose value should be updated.</param>
/// <param name="updateFunc">The function used to generate a new value for an existing key based on
/// the key's existing value.</param>
/// <param name="defaultValue">The value to be used for an absent key.</param>
/// <returns>The new or updated value for the key.</returns>
public static TValue AddOrUpdate <TKey, TValue>(
this IDictionary <TKey, TValue> target,
TKey key,
Func <TKey, TValue, TValue> updateFunc,
TValue defaultValue = default(TValue))
{
return(DictionaryUtils.AddOrUpdate(target, key, updateFunc, defaultValue));
}