std::unique_ptr is a smart pointer that exclusively owns a dynamically allocated object. Its destructor deletes the object by default, so ownership ends automatically when the pointer leaves scope or is reset. section 6.2.2
Use unique_ptr when one object should have one clear owner:
- Copying is disabled because copying would create a second owner; moving transfers ownership instead. section 6.2.2
- Store unique_ptr objects in containers to manage the pointed-to objects automatically when the container is destroyed. section 6.2.2
- Use operator-> to call members of the object owned by a unique_ptr. section 6.2.3
- Prefer unique_ptr over shared_ptr when shared ownership is unnecessary; shared_ptr adds shared ownership and a control-block count. section 6.2.2
Owning polymorphic blobs
A vector of std::unique_ptr<Blob> can hold different Blob implementations, such as StepperBlob and RandomBlob. The race moves each object through blob->step() and draws its current position through blob->total_steps(). section 6.2.3
Listing 6.13 Using smart pointers in a vector
void very_smart()
{
std::vector<SmartPointer<Blob>> blobs;
blobs.emplace_back(make_smart_pointer<StepperBlob>()); #1
} #2
This compact listing shows a smart-pointer vector taking ownership of a dynamically created StepperBlob and cleaning it up with the vector's lifetime. section 6.2.2
The pointer can also use a custom deleter. A coroutine task uses std::unique_ptr with a deleter that obtains a coroutine handle and calls destroy, allowing the task to follow the rule of zero. section 8.3.4
