Not twice as slow. But you are forgetting the case where you know the element is already in the map, and you want to call map.get() without wrapping it in an option.

C# does this fairly nicely with an "out" parameter: https://docs.microsoft.com/en-us/dotnet/api/system.collectio...

Or if you "know" it's there call the version that throws an exception if it isn't.

I haven't used that aspect of the Dictionary API at all in the 9 years programming C#, it is just too unwieldy to have to define a separate local variable to hold the result of the get. It also doesn't scope the out assignment (if the get fails, you can still read the out variable bound). I'm rarely in the case where I don't expect something to be in a map anyways, and when I do, I have an extension method with a default value returned if the key doesn't exist (or in some cases populate). Keeping expressions clean is important.