Why does this snippet using uniform initialization compile with g++4.6 but not g++4.7?

Question

Note that derived uses C++11 uniform initialization syntax to call the base class constructor.

class base
{
    protected:
        base()
        {}
};
         


        

Answer 1

Paolo Carlini, a GCC/libstdc++ contributor, confirmed it is a bug/regression.

Answer 2

compiling this with icpc ( intel compiler tested with version 11.1 -> 12.1) gives:

-bash-3.2$ icpc -std=c++0x test.c 
test.c(15): error: expected a declaration
          {}
          ^

test.c(12): error: expected a "("
              : base{} // <-- Note the c++11 curly brace syntax
                    ^

compilation aborted for test.c (code 2)

edit: but then again, c++11 is not fully implemented yet in icpc either http://software.intel.com/en-us/articles/c0x-features-supported-by-intel-c-compiler/

same as with g++ http://gcc.gnu.org/gcc-4.7/cxx0x_status.html

which clearly states it's still experimental, so a bug is very likely.

Answer 3

I found this:

"The draft says that an initializer list initializing a reference is done not by direct binding, but by first constructing a temporary out of the element in the initializer list, and then binding the target reference to that temporary"

So it might be choking on the fact that the temporary created by base{} is being done through a protected constructor.

Answer 4

It is probably because in version 4.7 C11 explicit override control was added.