CopyTo - KeyValuePair / dictionary extensions

KeyValuePairExtensions.cs

public static class KeyValuePairExtensions
{
    public static void CopyTo<TKey>(this IEnumerable<KeyValuePair<TKey, string>> keyValuePairs, IDictionary<TKey, string> target) => CopyTo(keyValuePairs, target, (a, b) => $"{a},{b}");
    
    public static void CopyTo<TKey, TValue>(this IEnumerable<KeyValuePair<TKey, TValue>> keyValuePairs, IDictionary<TKey, TValue> target, Func<TValue, TValue, TValue> aggregator)
    {
        foreach (var keyValuePair in keyValuePairs)
        {
            var key = keyValuePair.Key;
            
            if (target.TryGetValue(key, out var existing))
                target[key] = aggregator(existing, keyValuePair.Value);
            else
                target[key] = keyValuePair.Value;
        }
    }

    public static void CopyTo<TKey, TValue>(this IEnumerable<KeyValuePair<TKey, TValue>> keyValuePairs, IDictionary<TKey, TValue> target, bool overwrite)
    {
        if (overwrite)
            CopyOver(keyValuePairs, target);
        else
            CopyIfNotExists(keyValuePairs, target);
    }

    static void CopyOver<TKey, TValue>(IEnumerable<KeyValuePair<TKey, TValue>> keyValuePairs, IDictionary<TKey, TValue> target)
    {
        foreach (var keyValuePair in keyValuePairs)
            target[keyValuePair.Key] = keyValuePair.Value;
    }

    static void CopyIfNotExists<TKey, TValue>(IEnumerable<KeyValuePair<TKey, TValue>> keyValuePairs, IDictionary<TKey, TValue> target)
    {
        foreach (var keyValuePair in keyValuePairs)
        {
            if (target.ContainsKey(keyValuePair.Key))
                continue;

            target[keyValuePair.Key] = keyValuePair.Value;
        }
    }
}