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

simple/cpp/extract-method_after.cpp

@@ -0,0 +1,14 @@
+#include <print>
+
+void printBanner(){}
+std::string getOutstanding() { return "42.00"; }
+
+[[nodiscard]] std::string formatDetails(std::string_view name, std::string_view outstanding)
+{
+    return std::format("name: {}\namount: {}\n", name, outstanding);
+}
+
+void printDetails(std::string_view name) {
+    printBanner();
+    std::print("{}", formatDetails(name, getOutstanding()));
+}

simple/cpp/extract-method_before.cpp

@@ -0,0 +1,11 @@
+#include <iostream>
+#include <format>
+
+void printBanner(){}
+std::string getOutstanding() { return "42.00"; }
+
+void printDetails(std::string_view name) {
+    printBanner();
+    std::cout << std::format("name: {}\n", name);
+    std::cout << std::format("amount: {}\n",  getOutstanding());
+}

simple/cpp/extract-method_isolate-switch_after.cpp

@@ -0,0 +1,51 @@
+#include <algorithm>
+#include <variant>
+#include <vector>
+
+//Product.h
+struct Product
+{
+    double quantity;
+    double price;
+};
+
+//Discounts.h
+struct USDiscount {static constexpr double factor{0.85};};
+struct RUDiscount {static constexpr double factor{0.75};};
+struct CNDiscount {static constexpr double factor{0.9};};
+
+using Discount = std::variant<USDiscount, RUDiscount, CNDiscount>;
+
+//User.h
+struct User
+{
+    Discount discount;
+};
+
+
+// Order.h and Order.cpp if separating header from source
+class Order
+{
+public:
+    explicit Order(const User& user, std::vector<Product> products)
+        : user_{user}
+        , products_(std::move(products))
+    {}
+
+    [[nodiscard]] double calculateTotal() const
+    {
+        const double total = std::ranges::fold_left(products_, 0.0, [](double acc, const auto& product){return acc + (product.price * product.quantity);});
+        return applyRegionalDiscounts(total);
+    }
+
+    [[nodiscard]] double applyRegionalDiscounts(double total) const
+    {
+        return std::visit([total](const auto& discount) {
+            return total * discount.factor;
+        }, user_.discount);
+    }
+
+private:
+    User user_;
+    std::vector<Product> products_;
+};

simple/cpp/extract-method_isolate-switch_before.cpp

@@ -0,0 +1,47 @@
+#include <vector>
+
+enum class Country
+{
+    US,
+    RU,
+    CN
+};
+
+struct User
+{
+    Country country;
+};
+
+struct Product
+{
+    double quantity;
+    double price;
+};
+
+class Order
+{
+public:
+    explicit Order(const User& user, std::vector<Product> products)
+        : user_{user}
+        , products_(std::move(products))
+        {}
+    [[nodiscard]] double calculateTotal() const
+    {
+        double total = 0;
+        for (const auto& [quantity, price] : products_)
+        {
+            total += price * quantity;
+        }
+        switch (user_.country)
+        {
+        case Country::US: total *= 0.85; break;
+        case Country::RU: total *= 0.75; break;
+        case Country::CN: total *= 0.9; break;
+        }
+        return total;
+    }
+
+private:
+    User user_;
+    std::vector<Product> products_;
+};

simple/cpp/substitute-algorithm_after.cpp

@@ -0,0 +1,16 @@
+#include <algorithm>
+#include <optional>
+#include <string>
+#include <span>
+#include <array>
+
+std::optional<std::string> FoundPerson(std::span<const std::string> people)
+{
+    static constexpr std::array<std::string_view, 3> candidates{"Don", "John", "Kent"};
+
+    if (const auto it = std::ranges::find_first_of(people, candidates); it != people.end())
+    {
+        return *it;
+    }
+    return std::nullopt;
+}

simple/cpp/substitute-algorithm_before.cpp

@@ -0,0 +1,22 @@
+#include <string>
+#include <span>
+
+std::string FoundPerson(std::span<const std::string> people)
+{
+    for (const auto & person : people)
+    {
+        if (person == ("Don"))
+        {
+            return "Don";
+        }
+        if (person == ("John"))
+        {
+            return "John";
+        }
+        if (person == ("Kent"))
+        {
+            return "Kent";
+        }
+    }
+    return "";
+}