CppPatterns-Patterns/patterns/creational/builder.cpp at master · sftrabbit/CppPatterns-Patterns · GitHub

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// Builder

#include <vector>

class foo
{
  public:
    class builder;

    foo(int prop1, bool prop2, bool prop3, std::vector<int> prop4)
      : prop1{prop1}, prop2{prop2}, prop3{prop3}, prop4{prop4}
    { }

    int prop1;
    bool prop2;
    bool prop3;
    std::vector<int> prop4;
};

class foo::builder
{
  public:
    builder& set_prop1(int value) { prop1 = value; return *this; };
    builder& set_prop2(bool value) { prop2 = value; return *this; };
    builder& set_prop3(bool value) { prop3 = value; return *this; };
    builder& set_prop4(std::vector<int> value) { prop4 = value; return *this; };

    foo build() const
    {
      return foo{prop1, prop2, prop3, prop4};
    }

  private:
    int prop1 = 0;
    bool prop2 = false;
    bool prop3 = false;
    std::vector<int> prop4 = {};
};

int main()
{
  foo f = foo::builder{}.set_prop1(5)
                        .set_prop3(true)
                        .build();
}

// Separate the complex construction of an object from its
// representation.
//
// The `foo` class, on [5-18], has a complex construction process
// during which any subset of its properties might be set. This
// process is captured by the `foo::builder` class, on [20-38].
// This builder class provides an interface for
// constructing `foo` objects, allowing various combinations of
// parameters to be provided. This avoids having to define a large
// collection of constructors for `foo`.
//
// The `foo::builder` class implements a set of
// chainable functions for setting the construction parameters
// ([23-26]) and a `build` member function for constructing the `foo`
// object with these parameters ([28-31]).
//
// On [42-44], we use `foo::builder` to construct a `foo` object,
// setting its `prop1` and `prop3` members and calling `build` to
// construct the object.