5.5. DRY Impedance Mismatches

Have you ever experienced a telephone conversation with an annoying echo? That’s an impedance mismatch, caused when the signals aren’t perfectly synchronized. Impedance mismatch is a term from electrical engineering that has leaked over into the software world because it describes some of our problems.

In software, impedance mismatch is one of the common causes of DRY violations. An impedance mismatch occurs at the boundary of two abstraction styles: set-based to object-based, or procedural to object orientation. Because you try to reconcile the two abstraction styles, you end up with repetition around the boundaries.