CODEWITHSUNDEEP
c++oopstlinitializer-list
ejgallego
ejgallego

Reputation: 6852

Why I can't use a reference type inside a `std::initializer_list`

when I try to use an initializer list for a member that contains references, I get the following error:

no matching function for call to ‘std::vector<const Exp&>::vector(<brace-enclosed initializer list>)’

I have read several related posts, but first, they seem to get a different error; second, they qualify the use of references "as pointless".

Without getting into philosophical discussions, indeed I would appreciate knowing if it is possible to make the below example work:

#include <vector>

class Exp {
};

class Integer : public Exp {
public:
  const int value;
  Integer(const int val) : value(val) { }
};

int main() {

  const auto a1 = Integer(1);
  const auto a2 = Integer(2);

  const std::vector<const Exp&> va{a1,a2};
 }

Could it be a missing constructor for the vector class? Thanks a lot!

gcc (Ubuntu 5.3.1-14ubuntu2.1) 5.3.1 20160413

[Edited to remove spurious example]

Upvotes: 2

Views: 297

Answers (2)

ejgallego
ejgallego

Reputation: 6852

Thanks to everybody!!! I've settled on this solution for now:

std::array<const std::reference_wrapper<const Exp>, 2> ae{a1,a2};

I need to investigate more but I think that will do what I want for now.

Upvotes: 1

Brian Bi
Brian Bi

Reputation: 119069

Although this is not explicitly stated in the standard, attempting to use standard library containers to store non-object types should be regarded as undefined behaviour. See [container.requirements.general],

p1: "Containers are objects that store other objects..."

p4: "... X denotes a container class containing objects of type T..."

and so on.

Upvotes: 3

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