Concurrent Dictionary AddOrUpdate vs Index Add

Question

There are two ways I've assigned values to a existing key in a concurrent dictionary in my current project.

A. concurrentDictionary1[key] = value;

and

B. concurrentDictionary2.AddOrUpdate(key, value, (k, v) => value);

If I know that the 'key' exists, are these functionally equivalent?

Is protection offered by the concurrency of the Concurrent Dictionary bypassed with method 'A'?

What is the difference here? What are the reasons for choosing one over the other?

I looked through the documentation at msdn, and it seems they only initialize a concurrent dictionary with method 'A', not update it.

Answer 1

This is an old question, but no one answered why you would use one over the other.

Choose A (the indexer) if you want to add or update and the update is not dependent on the existing value.

Choose B (AddOrUpdate) if you want to add or update and the update depends on an existing value. AddOrUpdate will do the update atomically.

So in the case in the question, you want to use the indexer. It's simpler, easier to read, and probably faster since you aren't creating an anonymous function.