C++ Builder Examples

headers_builder_example.cpp

// A.h

class A {
public:
    int var;
    class Builder;
    A(Builder* builder);
    int getVar();
    Builder* newBuilder();
};

// Builder.h

class A::Builder {
public:
    int var;
    Builder();
    Builder(A* a);
    Builder withVar(int var);
    A* build();
};

// A.cpp

A::A(Builder* builder) {
    var = builder->var;
}

int A::getVar() {
    return var;
}

A::Builder* A::newBuilder() {
    return new Builder(this);
}

// Builder.cpp

A::Builder::Builder() {
    var = 0;
}

A::Builder::Builder(A* a) {
    var = a->var;
}

A::Builder A::Builder::withVar(int var) {
    this->var = var;
    return *this;   
}

A* A::Builder::build() {
    return new A(this);
}

// Example usage
int main(void) {

    auto *a = A::Builder()
        .withVar(123)
        .build();

    return 0;
}

inlined_builder_example.cpp

class A {
private:
    int var;
    
public:
    class Builder;
    
    A(Builder* builder) {
      var = builder->var;
    }
    
    int getVar() {
        return var;
    }
    
    Builder* newBuilder() {
        return new Builder(this);
    }
    
    class Builder {
    public:
        int var;
        
        Builder() { 
            var = 0;
        }
        
        Builder(A* a) {
            var = a->var;
        }
        
        Builder withVar(int var) {
            this->var = var;
            return *this;   
        }
        
        A* build() {
            return new A(this);
        }
    };
};

// Example usage
// g++ test.cpp -std=c++11 -o test.o && ./test.o
int main(void) {

    auto *a = A::Builder()
        .withVar(123)
        .build();
  
    return 0;
}