How should anonymous types be used in C#?

anonymous-types, c#

Solution

Anonymous types have nothing to do with the design of systems or even at the class level. They're a tool for developers to use when coding.

I don't even treat anonymous types as types per-se. I use them mainly as method-level anonymous tuples. If I query the database and then manipulate the results, I would rather create an anonymous type and use that rather than declare a whole new type that will never be used or known outside of the scope of my method.

For instance:

var query = from item in database.Items
            // ...
            select new { Id = item.Id, Name = item.Name };

return query.ToDictionary(item => item.Id, item => item.Name);

Nobody cares about `a, the anonymous type. It's there so you don't have to declare another class.

Problem

I've seen lots of descriptions how anonymous types work, but I'm not sure how they're really useful. What are some scenarios that anonymous types can be used to address in a well-designed program?

Original source