While trying to add items to a dictionary I discovered that there’s no equivalent of the AddRange which is available for lists.

This is for good reason as adding a KeyValuePair to a dictionary requires first checking that the given key doesn’t already exist and so is more computationally expensive than simply appending to the end of a list.

However, in my case I knew that the items didn’t already exist (and added an option to ignore them if they did).

I also wanted to be able to return a null value form a dictionary if the specified key doesn’t exist, rather than throwing an error when trying to access the value.

To solve both these problems I created the below extension to add the required methods to the Dictionary class.

public static class DictionaryExtensions
{
	public static void AddRange<TKey, TValue>(this Dictionary<TKey, TValue> dictionary, List<KeyValuePair<TKey, TValue>> itemsToAdd, bool ignoreExisting = true)
	{
		if (ignoreExisting)
		{
			itemsToAdd.Where(x => !dictionary.ContainsKey(x.Key)).ToList().ForEach(x => dictionary.Add(x.Key, x.Value));
		}
		else
		{
			itemsToAdd.ForEach(x => dictionary.Add(x.Key, x.Value));
		}
	}

	public static TValue GetValueOrDefault<TKey, TValue>
		(this IDictionary<TKey, TValue> dictionary, TKey key) =>
		dictionary.TryGetValue(key, out var returnValue) ? returnValue : default;
}

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