Is there any function like computeIfAbsent in Java

[tasty0tomato]

https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#computeIfAbsent-K-java.util.function.Function-
It seems easy to use this function to do Add operation like this
buckets.computeIfAbsent(word.length(), x -> new ArrayList()).add(word);
But in C#, and maybe because I am not much familiar with C#, I need to write these code.

if (!buckets.ContainsKey(word.Length))
{
   buckets.Add(word.Length, new List<string>());
}
buckets[word.Length].Add(word);

And there was a similar question in Stack, but unfortunately, there wasn't an answer.

[gfoidl]

You can write it in C# with very efficiently. See the following example:

using System.Runtime.InteropServices;

Dictionary<int, List<string>> buckets = new();

AddToBucket(buckets, "Hello");
AddToBucket(buckets, "World");
AddToBucket(buckets, "C# rocks :-)");

foreach (KeyValuePair<int, List<string>> bucket in buckets.OrderBy(b => b.Key))
{
    Console.WriteLine($"bucket: {bucket.Key}");

    foreach (string item in bucket.Value)
    {
        Console.WriteLine($"\t{item}");
    }
}

static void AddToBucket(Dictionary<int, List<string>> buckets, string word)
{
    ref List<string>? list = ref CollectionsMarshal.GetValueRefOrAddDefault(buckets, word.Length, out _);
    list ??= new List<string>();

    list.Add(word);
}

very efficiently.

---

Different approach:

static void AddToBucket(Dictionary<int, List<string>> buckets, string word)
{
    List<string> entries = buckets.GetValueOrDefault(word.Length, new List<string>());

    entries.Add(word);
    buckets[word.Length] = entries;
}

[tasty0tomato]

Wow, I do not even know CollectionsMarshal. And what a pity there isn't much information about it except .NET API browser.

[Joe4evr]

Yeah, CollectionsMarshal is pretty new.