Find-or-insert with only one lookup in c# dictionary

Question

I\'m a former C++/STL programmer trying to code a fast marching algorithm using c#/.NET technology...

I\'m searching for an equivalent of STL method \"map::insert\"

Answer 1

Old question, but I may have just stumbled across an acceptable solution. I use a combination of TryGetValue, ternary operator and index assignment.

var thing = _dictionary.TryGetValue(key, out var existing) ? existing : _dictionary[key] = new Thing(); 

I have written a small example for that.

class Program
{
    private static readonly Dictionary _translations
        = new Dictionary() { { "en", "Hello world!" } };

    private static string AddOrGetTranslation(string locale, string defaultText)
        => _translations.TryGetValue(locale, out var existingTranslation)
            ? existingTranslation
            : _translations[locale] = defaultText;

    static void Main()
    {
        var defaultText = "#hello world#";

        Console.WriteLine(AddOrGetTranslation("en", defaultText)); // -> Hello world!

        Console.WriteLine(AddOrGetTranslation("de", defaultText)); // -> #hello world#
        Console.WriteLine(AddOrGetTranslation("de", "differentDefaultText")); // -> #hello world#

        _translations["de"] = "Hallo Welt!";
        Console.WriteLine(AddOrGetTranslation("de", defaultText)); // -> Hallo Welt!
    }
}