Everything else is just a tool to model your domain in a way that’s easier to read and reason about, and to produce much shorter code. Interfaces define module boundaries and can be mocked to enable simpler testing. Through classes, objects, and data structures, you can model your domain entities. Enums make a list of limited options crystal clear. Extensions allow you to add functionality to existing types, without having access to their original source code, giving advantage of better logic structure. With generics, you can write universal code, promoting reuse. And overloaded operators give that extra edge to common operations that benefit from succinct, crisp syntax.
Type alias
Most simple custom type imaginable – a new name for an existing type. It can be used to shorten type names or convey more meaning, but doesn’t actually create a new type.