Code Ranges: A Deeper Look at Ruby Strings - Shopify

This post provides a deep dive into Ruby's string implementation, specifically focusing on encoding-aware strings and the 'code range' mechanism. It explains how the code range is used to optimize string operations by caching information about character validity and boundaries. The post details the four code range values (`ENC_CODERANGE_UNKNOWN`, `ENC_CODERANGE_7BIT`, `ENC_CODERANGE_VALID`, `ENC_CODERANGE_BROKEN`), their mapping to Ruby methods, and how they are stored and managed across different Ruby implementations (MRI, JRuby, TruffleRuby). It also discusses how string operations can affect the code range and the strategies used to avoid unnecessary recalculations, such as lazy calculation and reasoning about code range preservation during operations. The post also touches upon the concept of 'single-byte optimizable' strings and how it relates to code range optimizations.