Created
May 17, 2014 11:10
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baseless polymorphism in C++11
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// http://channel9.msdn.com/Events/GoingNative/2013/Inheritance-Is-The-Base-Class-of-Evil | |
#include <iostream> | |
#include <memory> | |
#include <string> | |
#include <vector> | |
// ===== library ==== | |
class Document | |
{ | |
public: | |
class Object | |
{ | |
private: | |
class Concept | |
{ | |
public: | |
virtual ~Concept() = default; | |
virtual void draw_(std::ostream&, std::size_t) const = 0; | |
}; | |
template <typename T> | |
class Model | |
: public Concept | |
{ | |
private: | |
T data_; | |
public: | |
Model(T x) | |
: data_(std::move(x)) | |
{} | |
void draw_(std::ostream& out, std::size_t position) const override | |
{ | |
data_.draw(out, position); | |
} | |
}; | |
std::shared_ptr<const Concept> self_; | |
public: | |
template <typename T> | |
Object(T x) | |
: self_{std::make_shared<Model<T>>(std::move(x))} | |
{} | |
void draw(std::ostream& out, std::size_t position) const | |
{ | |
self_->draw_(out, position); | |
} | |
}; | |
std::vector<Object> objects; | |
void draw(std::ostream& out, std::size_t position) const | |
{ | |
out << std::string(position, ' ') << "<document>" << std::endl; | |
for (const auto& e : objects) | |
e.draw(out, position + 2); | |
out << std::string(position, ' ') << "</document>" << std::endl; | |
} | |
}; | |
// ====== user ====== | |
class MyClass | |
{ | |
public: | |
int i; | |
void draw(std::ostream& out, std::size_t position) const | |
{ | |
out << std::string(position, ' ') << "MyClass " << i << std::endl; | |
} | |
}; | |
int main() | |
{ | |
Document document; | |
document.objects.emplace_back(MyClass{1}); | |
document.objects.emplace_back(document); | |
document.objects.emplace_back(MyClass{2}); | |
document.draw(std::cout, 0); | |
} |
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