How to create a vector with non-copyable and non-assignable objects?

Question

I have a class

class A {
 public:
  A(int x): x_(x) {}
  void SetValue(int m) {x_=m};
 private:
   DISALLOW_COPY_AND_ASSIGN(A);
};

I'm trying to create a vector of objects of type A

vector<std::unique_ptr<A>> objects;
objects.reserve(10);
for (int i = 0; i < 10; i++) {
   auto a = MakeUnique<A>();
   a->SetValue(20);
   objects.emplace_back(a);
}

This results in a compilation error call to deleted constructor of 'std::unique_ptr<A, std::default_delete<A> >'

`DISALLOW_COPY_AND_ASSIGN(A)` should not be a macro that defines the copy ctor and assign operator, it should be a base class that mark the copy and assign operator as deleted, and defaulting move operations. — Guillaume Racicot, Oct 10 '17 at 18:50
@GuillaumeRacicot, while I always drive from boost noncopyable, I fail to see the advantage of your assertion / axiom above the macro — Werner Erasmus, Oct 11 '17 at 08:57

score 7 · Accepted Answer · answered Oct 10 '17 at 18:45

7

std::unique_ptr is not copyable, so you need to move it into the container:

for (int i = 0; i < 10; i++) {
   auto a = MakeUnique<A>();
   a->SetValue(20);
   objects.emplace_back(std::move(a));
}

answered Oct 10 '17 at 18:45

Angew is no longer proud of SO

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Possible alternative with C++17: `auto & a = objects.emplace_back(MakeUnique()); a->SetValue(20);` – Xirema Oct 10 '17 at 18:47
`objects.emplace_back(MakeUnique()); objects.back()->SetValue(20);` – rustyx Oct 10 '17 at 19:03
@Xirema While equivalent in this case, in general it would have different behaviour for cases where `SetValue` can throw an exception. I generally prefer to fully set up objects before handing them over to a contaier. – Angew is no longer proud of SO Oct 10 '17 at 19:07
@RustyX See my previous comment: equivalent in this case, different when exceptions are possible. – Angew is no longer proud of SO Oct 10 '17 at 19:07

How to create a vector with non-copyable and non-assignable objects?

1 Answers1