Sum types are much more direct than other variants in a language that effectively implements them. For example, in Rust, who's `enum`s are effectively sum type

Sum types are much more direct than other variants in a language that effectively implements them. For example, in Rust, who's `enum`s are effectively sum types, we can take advantage of the type system while using channels that are well-typed. https://github.com/servo/servo/blob/master/components/msg/constellation_msg.rs#L197-L214 https://github.com/servo/servo/blob/master/components/msg/co... pub enum Msg { ExitMsg, FailureMsg(Failure), InitLoadUrlMsg(Url), LoadCompleteMsg, FrameRectMsg(PipelineId, SubpageId, Rect<f32>), LoadUrlMsg(PipelineId, LoadData), ScriptLoadedURLInIFrameMsg(Url, PipelineId, SubpageId, IFrameSandboxState), NavigateMsg(NavigationDirection), PainterReadyMsg(PipelineId), ResizedWindowMsg(WindowSizeData), KeyEvent(Key, KeyState, KeyModifiers), /// Requests that the constellation inform the compositor of the title of the pipeline /// immediately. GetPipelineTitleMsg(PipelineId), /// Requests that the constellation inform the compositor of the a cursor change. SetCursorMsg(Cursor), } Here we can define a sum type called `Msg` that has various variants. These are the only thing a channel constraint to that type can consume. Each destructing or pattern matching has to cover all possible cases, otherwise it's a compiler error. This makes it effortless to have complex communication where the data is composed of multiple things, multiple types. [1] Here's another example of a sum type being used as a messaging type in Servo. [2] Shows pattern matching on all variants and variants of variants, which produces well-typed code. [1]: https://github.com/servo/servo/blob/master/components/net/resource_task.rs#L134-L139 https://github.com/servo/servo/blob/master/components/net/re... [2]: https://github.com/servo/servo/blob/master/components/net/resource_task.rs#L171-L175 https://github.com/servo/servo/blob/master/components/net/re... I probably use `enum`s pretty frequently, especially when working with channels. I don't use primitive types-based channels too often come to think of it.