True mastery of Rust begins with the DRY (Don't Repeat Yourself) principle. Before we reach for generic syntax, we must traverse the path of Concrete Abstraction. Imagine a retail app comparing prices (i32) and sensor temperatures (f32); copy-pasting the comparison logic creates technical debt where bugs flourish in the shadows of duplication.

1. The Refactoring Workflow

To move from duplication to elegance, follow the three-step extraction: Identify repeated logic, Extract that logic into a function body with clear inputs/outputs, and Update the original call sites to use the new function.

2. The Limits of Concrete Logic

While Listing 10-3 successfully abstracts logic, it remains bound to Concrete Data Types. It solves logic duplication but leaves us vulnerable to Type Duplication. This ceiling is the catalyst for Abstract Types ($$), where logic is finally freed from specific memory layouts.