Scala Collections are amazingly powerful and cleverly designed, but often don't perform good enough for computation-intensive tasks, spurring various efforts in the Scala ecosystem to improve the situation. This talks explains some problems behind these performance issues, and details the approach and trade-offs chosen in Scalaxy/Streams's compiler plugin and macros to tackle them. It also reveals some pitfalls of such optimizations, and hacks that can be used to write similar non-trivial macros. https://github.com/ochafik/Scalaxy/tree/master/Streams