Add C++ refactoring examples (C++23/26)

[chibi-dogs]

Summary

This PR ports some of the existing examples in Java to C++. I have added before and after examples for the following 3 techniques:

• Extract Method
• Extract Method – Isolate Switch
• Substitute Algorithm

All examples compile when tested with clang trunk and using C++26. The before files are a direct, idiomatic C++ translation of the Java originals. The after files apply the refactoring and additionally adopt several modern C++ idioms where I felt appropriate.

Design decisions & deviations from Java originals

I was having trouble porting some of the solutions to C++ since many things that may be considered idiomatic in Java don't necessarily have 1 to 1 mappings in C++. I made the following decisions:

Substitute Algorithm

• before: raw if-chain returning "" on failure — true to the Java original
• after: replaces the chain with std::ranges::find_first_of over a static constexpr std::array<std::string_view>, and returns std::optional<std::string> instead of an empty string sentinel.
• Rationale: empty-string-as-failure has no idiomatic equivalent in modern C++ so I used std::optional. I think that using ranges find_first_of is really nice since it expresses the algorithm's intent quite clearly.

Extract Method – Isolate Switch

• before: raw loop + switch on an enum, applying a discount factor
• after: replaces the switch with std::variant + std::visit over typed discount structs, each holding a static constexpr double factor; total is computed via std::ranges::fold_left
• Rationale: C++ has no pattern matching to the best of my knowledge unless you just use if/else with strings. I therefore decided to use std::variant + std::visit which also would fit Replace Conditional with Polymorphism quite nicely.

Extract Method (basic)

• std::print might not work for older versions of C++ and certain compilers.
• std::cout << std::format() << std::endl would work even for older versions of the language and compilers so it might be a better choice. But I decided to go ahead with std::print since the name carries the intent a lot better in my opinion.

Notes

• Targets C++23/26 (std::print, std::ranges::fold_left, std::ranges::find_first_of, std::span)
• Added [[nodiscard]] when appropriate even though it adds some "noise". I added it to the signature of all functions that return values since looking at clang tidy complaining about it was stressing me out 😅

Happy to discuss these design decisions! 😄