問題：
I can see in the API docs for Predef that they're subclasses of a generic function type (From) => To, but that's all it says. 我可以在Predef的API文檔中看到它們是通用函數類型（From）=> To的子類，僅此而已。 Um, what? 嗯什麼？ Maybe there's documentation somewhere, but search engines don't handle "names" like "<:<" very well, so I haven't been able to find it. 也許某處有文檔，但是搜索引擎不能很好地處理“ <：<”之類的“名稱”，因此我找不到它。
Follow-up question: when should I use these funky symbols/classes, and why? 後續問題：什麼時候應該使用這些時髦的符號/類，爲什麼？
解決方案：
參考一： https://en.stackoom.com/question/ENbl參考二： https://stackoom.com/question/ENbl