C++ move into container

Question

I have a class like this:

class Object {
   ...
}

and a container which essentially consists of a std::vector<Object>:

class ObjectContainer {
public: 
    void addObject(Object ?? object);
    ...
private:
    std::vector<Object> vector;
}

Now after I have initialized an Object instance I would like to add the instance to the container and forget about i.e. something like:

Container container;
{
    Object object(args...);
    // Maybe more object initialization

    container.addObject( object );
}

Now - if possible I would like the container, i.e. std::vector<Object> to 'take' the current object instance without any copying - is this possible? And would the implementation of Container::addObject be as simple as:

void Container::addObject( Object && object) {
   vector.push_back( object );
}

try container.addObject( std::move(object) );, keeping the definition as addObject(Object && object) — iavr
– iavr, Commented Jul 30, 2015 at 22:29
I assume Object is cheap to move otherwise you won't get much benefit from this. — Chris Drew
– Chris Drew, Commented Jul 31, 2015 at 1:59

Nir Friedman · Accepted Answer · 2015-07-30 22:44:38Z

3

It wouldn't be quite that simple, you need one more thing:

void Container::addObject( Object && object) {
   vector.push_back(std::move(object));
}

Within the addObject function, object itself is actually an lvalue, you have to cast it back to an rvalue.

answered Jul 30, 2015 at 22:44

Nir Friedman

17.9k2 gold badges48 silver badges77 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

fredoverflow · Accepted Answer · 2015-07-30 22:58:50Z

1

Instead of preparing the object and then move it into the container as the last step, why not create the object inside the container to begin with and the continue messing around with it?

Here is how you would do it with a std::vector directly:

std::vector<Object> vector;
vector.emplace_back(args...);
Object& object = vector.back();

Then you can do further initialization stuff with object which is already part of the vector.

answered Jul 30, 2015 at 22:58

fredoverflow

265k101 gold badges403 silver badges680 bronze badges

1 Comment

user422005 Over a year ago

Yes - I might actually do it this way; I know learned about vector.emplace_back()- that was new to me. Thank you.

Collectives™ on Stack Overflow

C++ move into container

2 Answers 2

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related