How to store a vector of objects of an abstract class which are given by std::unique_ptr?

Question

I got a loop in which i use a function returning std::unique_ptr to an object of an abstract class. I want to store these objects into a std::vector via push_back. But since the objects are of abstract type i get the following error:

error: cannot allocate an object of abstract type

for the line

  cells.push_back(std::move(*cell));

where cells is a std::vector of the abstract type and cell is of type

std::unique_ptr<AbstractType>&& cell

(I actually pass cell to a handler class) I know that one can not instantiate an abstract type and as I'm understanding the std:move operator it need to instantiate the object somehow?

Can anybody help me how to manage the problem? Or should the function (not my part of the project) not return a unique pointer to an object of an abstract type?

Are we talking about a `vector`? That won't work. Store a `vector>` instead. — R. Martinho Fernandes, Aug 30 '12 at 19:15
You are right! I was blind, I changed it to `vector>` and now it works — soriak, Aug 30 '12 at 19:48
@R.MartinhoFernandes: +1 on your comment (that should be an answer). You must read minds! — Howard Hinnant, Aug 30 '12 at 19:50
Why is `cell` an rvalue reference? That sounds wrong. Can we see more code? — fredoverflow, Aug 30 '12 at 19:58

score 9 · Accepted Answer · answered Aug 30 '12 at 19:54

9

You can't store AbstractType elements directly on a std::vector. You can simply store the unique_ptrs themselves in a std::vector<std::unique_ptr<AbstractType>> with cells.push_back(std::move(cell)).

answered Aug 30 '12 at 19:54

R. Martinho Fernandes

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The reason being that you are invoking the copy constructor, and thus trying to instantiate an abstract class. – Alexandre C. Aug 30 '12 at 20:30

How to store a vector of objects of an abstract class which are given by std::unique_ptr?

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