Strings are used pervasively in Ruby. If we can make them faster, we can make many apps faster.

In this talk, I will be introducing ropes: an immutable tree-based data structure for implementing strings. While an old idea, ropes provide a new way of looking at string performance and mutability in Ruby. I will describe how we replaced a byte array-oriented string representation with a rope-based one in JRuby+Truffle. Then we’ll look at how moving to ropes affects common string operations, its immediate performance impact, and how ropes can have cascading performance implications for apps.