GCC refuses list initialisation of parameter

Question

I have the following code:

#include <initializer_list>
#include <utility>

enum class Classification
{
  Unspecified,
  Primary,
  Secondary
};

class ClassificationMap
{
public:
  ClassificationMap(std::initializer_list<std::pair<const Classification, int>> content = {});
};

void foo(ClassificationMap) {}

int main()
{
    foo({{Classification::Unspecified, 42}});
}

Visual Studio 2013 & 2017 and Clang 3.4.1 (and above) both compile the code just fine. From my POV, it should be fine as well. However, GCC 5.1 refuses to compile it, with the following error:

<source>: In function 'int main()':
<source>:22:44: error: could not convert '{{Unspecified, 42}}' from '<brace-enclosed initializer list>' to 'ClassificationMap'
     foo({{Classification::Unspecified, 42}});

[Live example]

(I am passing the correct standard flag (-std=c++11) to both GCC and Clang).

Is there a problem in my code, or is this actually a GCC bug?

---

Supplemental info: in my real code, the initialiser list is used to initialise an unordered map member of the ClassificationMap class (that's why its type is what it is). I need the code to work in VS2013 & GCC 5.1

Answer 1

Here is a good workaround for the issue (abandon default value):

class ClassificationMap
{
public:
    ClassificationMap(std::initializer_list<std::pair<const Classification, int>> content);
    ClassificationMap() : ClassificationMap({}) {}

};

You will have exact behavior you want and it compiles everywhere.

https://godbolt.org/g/WUuMzP