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Ownership semantics for pointers in C++
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| #include <iostream> | |
| #include <memory> | |
| using namespace std; | |
| class Resource { | |
| public: | |
| Resource(string id) : _id(id) { | |
| cout << "Resource::Resource(" << _id << ")" << endl; | |
| } | |
| ~Resource() { | |
| cout << "Resource::~Resource(" << _id << ")" << endl; | |
| } | |
| void Speak() { | |
| cout << "Resource::Speak(" << _id << ")" << endl; | |
| } | |
| private: | |
| string _id; | |
| }; | |
| class ResourceBuilder { | |
| public: | |
| ResourceBuilder() { | |
| cout << "ResourceBuilder::ResourceBuilder()" << endl; | |
| } | |
| ~ResourceBuilder() { | |
| cout << "ResourceBuilder::~ResourceBuilder()" << endl; | |
| } | |
| unique_ptr<Resource> Build(string id) { | |
| return unique_ptr<Resource>(new Resource(id)); | |
| } | |
| shared_ptr<Resource> BuildShared(string id) { | |
| return shared_ptr<Resource>(new Resource(id)); | |
| } | |
| }; | |
| class ResourceConsumer { | |
| public: | |
| ResourceConsumer() { | |
| cout << "ResourceConsumer::ResourceConsumer()" << endl; | |
| } | |
| ~ResourceConsumer() { | |
| cout << "ResourceConsumer::~ResourceConsumer()" << endl; | |
| } | |
| void ConsumeWithoutOwnership(Resource* const resource) { | |
| resource->Speak(); | |
| } | |
| void ConsumeWithOwnership(const unique_ptr<Resource> resource) { | |
| resource->Speak(); | |
| } | |
| void ConsumeWithSharedOwnership(const shared_ptr<Resource> resource) { | |
| resource->Speak(); | |
| } | |
| }; | |
| int main(int argc, char* argv[]) { | |
| /* | |
| Output: | |
| ResourceBuilder::ResourceBuilder() | |
| Resource::Resource(resource1) | |
| Resource::Resource(resource2) | |
| Resource::Resource(resource3) | |
| ResourceConsumer::ResourceConsumer() | |
| Resource::Speak(resource1) | |
| Resource::Speak(resource2) | |
| Resource::~Resource(resource2) | |
| Resource::Speak(resource3) | |
| Resource::Resource(resource4) | |
| Resource::Speak(resource4) | |
| Resource::~Resource(resource4) | |
| -- main going out of scope -- | |
| ResourceConsumer::~ResourceConsumer() | |
| Resource::~Resource(resource3) | |
| Resource::~Resource(resource1) | |
| ResourceBuilder::~ResourceBuilder() | |
| */ | |
| unique_ptr<ResourceBuilder> builder(new ResourceBuilder); | |
| auto resource1 = builder->Build("resource1"); | |
| auto resource2 = builder->Build("resource2"); | |
| auto resource3 = builder->BuildShared("resource3"); | |
| unique_ptr<ResourceConsumer> consumer(new ResourceConsumer); | |
| consumer->ConsumeWithoutOwnership(resource1.get()); // raw pointer (ownership not assumed) | |
| consumer->ConsumeWithOwnership(std::move(resource2)); // lvalue, have to be moved | |
| consumer->ConsumeWithSharedOwnership(resource3); // shared | |
| consumer->ConsumeWithOwnership(builder->Build("resource4")); // rvalue | |
| cout << "-- main going out of scope --" << endl; | |
| return 0; | |
| } |
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