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. — Useless
– Useless, Commented Feb 23, 2017 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
– Baum mit Augen ♦, Commented Feb 23, 2017 at 15:16

Quentin · Accepted Answer · 2017-02-23 15:15:05Z

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;

Vittorio Romeo · Accepted Answer · 2017-02-23 15:27:54Z

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));

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