C# Best Practices – Why Use string.Empty Over Double Quotes?

If you insist of having your object to immutable, there is obviously no other way than providing the 20 strings through the constructor. And if you want to be able to leave some of the strings out, you must say which arguments you are providing and which are not, which leads you to some form of named parameters. Of course, besides the possibilities you mentioned by yourself, you can also

• provide the 20 arguments by a list of strings
• provide them by a dictionary (key=>value, where "key" is the attribute name)
• provide them by an object of a helper class, which has the same 20 properties with getters and setters, so this one won't be immutable

It may also be a good idea to implement Equals and GetHashCodeby utilizing reflection, looping over all public string properties of your class.

That's an interesting take on the factory pattern. I like the combination of the Dictionary and the lambda expression; it made me look at that container in a new way.

I'm ignoring the concern in your question about CPU cycles as you mentioned in the comments that the non-lambda approach doesn't provide what you need.

I think either approach (switch vs. Dictionary + lambda) is going to be fine. The only limitation is that by using the Dictionary, you are limiting the types of inputs you could receive in order to generate the returned class.

Using a switch statement would provide you more flexibility on input parameters. However, if this got to be an issue, you could wrap the Dictionary inside of a method and have the same end result.

If it's new for your team, comment the code and explain what's going on. Call for a team code review, walk them through what was done and make them aware of it. Other than that, it looks fine.