Reference destructing object before use

Question

I'd like to create an object using a

object().addSomething().addSomethingElse()

syntax and then use it in a part of the code, but the following code won't work:

class myObj {
public:
 myObj() {}
 ~myObj() { std::cout << "dtor called" << std::endl; }
 myObj& someOtherOperation() {
  return *this;   
 }
};

int main() {
    auto& elementRef = myObj().someOtherOperation();
    {
        std::cout << "some stuff that uses elementRef" << std::endl;
    }  
}

the destructor is called before the part of the code that uses the reference.

I would like to avoid an expensive object copy operation and keeping the

object().addSomething().addSomethingElse()

syntax, but it seems references don't allow for that. Any solutions to this?

Answer 1

Create the object independently:

auto o = myObj();

and then use it freely:

o.someOtherOperation().someOtherOperation();

Answer 2

You can optimize by using move semantics when the implicit object parameter is an rvalue:

myObj someOtherOperation() & {
    return *this;   
}

myObj someOtherOperation() && {
    return std::move(*this);   
}

An example of the difference:

auto element = myObj().someOtherOperation(); //uses move semantics
myobj obj;
auto otherElement = obj.someOtherOperation(); //doesn't use move semantics