Modern C++ Programming with Test-Driven Development

2.16 Refactoring to Single-Responsibility Functions

The ​encodedDigits​ function continues to increase in complexity. We inserted blank lines in order to visually group related statements, a dead giveaway that a function does too much.

The ​ single responsibility principle​ (SRP) tells us that each function should have one reason to change.[7]  ​encodedDigits​ exhibits a classic violation of the SRP: it mixes high-level policy with implementation details.

Our ​encodedDigits​ function accomplishes its goal using a two-step algorithm. First append the encoded first letter to the encoding, and then iterate through the rest of the letters and append them. The problem is that ​encodedDigits​ also includes the low-level details to accomplish those ...