c++ - Implicitly deleted default constructor works in C++14 -

i doing tests code did not compile, , discovered code:

struct {     a(int) {};     virtual void foo() = 0; };  struct b : public virtual {     virtual void bar() = 0; };  struct c : public b {     c() : a(1) {}     virtual void foo() override {}     virtual void bar() override {} };  int main() {     c c;     return 0; } 

in c++11 fails compile (on g++ 7.0.1) ‘b::b()’ implicitly deleted because default definition ill-formed, while in c++14 compiles successfully.

i've tried find out new feature of c++14 allowed work, no avail. description in cppreference not mention of sort seems.

why can code compile in c++14 not in c++11?

definitively it's bug in gcc 7 because when have checked out code in online compiler gcc 7+, has worked without kind of problem.

so here give ide online can set favorite compiler , try tests, if want.

https://godbolt.org/

sorry can't better couldn't reproduce error.