C++ unique_ptr vector

Question

I have the following line of code

SystemFactory::system_ptr system = _Factory->createSystem(systemType);
_Systems.push_back(std::move(system));

The problem that I have is I can't just return the system as it will NULL it after moving it. The solution that I came with is the following and I don't know if it's the best one.

return (_Systems.end() - 1)->get();

If there is a better way of doing this?

Names like `_Factory` and `_Systems` are IIRC [reserved for the implementation in all scopes](http://stackoverflow.com/a/228797/212858). — Useless, Feb 23 '17 at 15:16
OT: `_Systems` is an implementation reserved identifier, you cannot use it. Also, starting variable names with an uppercase letter is somewhat uncommon. — Baum mit Augen, Feb 23 '17 at 15:16
Link to rules for naming [identifiers](http://en.cppreference.com/w/cpp/language/identifiers). — IInspectable, Feb 23 '17 at 15:17

score 8 · Answer 1 · answered Feb 23 '17 at 15:15

8

You can either use back():

return _Systems.back().get();

... or save it beforehand:

SystemFactory::system_ptr system = _Factory->createSystem(systemType);
auto *p = system.get();
_Systems.push_back(std::move(system));
return p;

answered Feb 23 '17 at 15:15

Quentin

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score 4 · Answer 2 · answered Feb 23 '17 at 15:27

In C++17, std::vector::emplace_back will return a reference to the emplaced object. Therefore you'll be able to write:

SystemFactory::system_ptr system = _Factory->createSystem(systemType);
return _Systems.emplace_back(std::move(system));

Or even shorter:

return _Systems.emplace_back(_Factory->createSystem(systemType));

C++ unique_ptr vector

2 Answers2