feat: builder pattern

Builder/main.cpp

@@ -1,8 +1,101 @@
 #include <iostream>
+#include <memory>
+#include <numeric>
+#include <vector>
+
+std::string join(const std::vector<std::string> &values,
+                 const std::string &separator) {
+  if (values.empty()) {
+    return "";
+  } else {
+    return std::accumulate(
+        std::next(values.begin()), values.end(), values.front(),
+        [&separator](const std::string &left, const std::string &right) {
+          return left + separator + right;
+        }
+
+    );
+  }
+}
+
+class Product {
+public:
+  std::vector<std::string> parts;
+
+  void listParts() const {
+    std::cout << "Parts: " << join(parts, ", ") << std::endl;
+  }
+};
+
+class Builder {
+public:
+  virtual ~Builder() = default;
+  virtual const Builder &addPartA() const = 0;
+  virtual const Builder &addPartB() const = 0;
+  virtual const Builder &addPartC() const = 0;
+};
+
+class ConcreteBuilder : public Builder {
+private:
+  Product *product = nullptr;
+
+public:
+  ConcreteBuilder() { reset(); }
+  ~ConcreteBuilder() { delete product; }
+
+  void reset() {
+    if (product != nullptr) {
+      delete product;
+    }
+    product = new Product();
+  }
+
+  const Builder &addPartA() const override {
+    product->parts.push_back("Part A");
+    return *this;
+  }
+  const Builder &addPartB() const override {
+    product->parts.push_back("Part B");
+    return *this;
+  }
+  const Builder &addPartC() const override {
+    product->parts.push_back("Part C");
+    return *this;
+  }
+
+  Product *getProduct() {
+    Product *result = product;
+    product = nullptr;
+    return result;
+  }
+};
+
+class Director {
+private:
+  Builder *builder = nullptr;
+
+public:
+  Director(Builder *builder) : builder(builder) {}
+
+  void buildSimpleProduct() { builder->addPartA(); }
+  void buildFullProduct() { builder->addPartA().addPartB().addPartC(); }
+};
 
 int main(int argc, char *argv[]) {
 
   std::cout << "Builder" << std::endl;
 
+  ConcreteBuilder builder = ConcreteBuilder();
+  Director director(&builder);
+
+  director.buildSimpleProduct();
+  auto simple_product = std::unique_ptr<Product>(builder.getProduct());
+  simple_product->listParts();
+
+  builder.reset();
+  director.buildFullProduct();
+  auto full_product = std::unique_ptr<Product>(builder.getProduct());
+  full_product->listParts();
+
   return EXIT_SUCCESS;
 }