I am trying to overload operators for std::initializer_list, but the following compiles neither in GCC 4.7.2 nor Clang 3.2:

#include <initializer_list>

void operator+(const std::initializer_list<int>&, const std::initializer_list<int>&);

int main() {
   {1, 2} + {3, 4};
}

13.5/6 says that an operator function shall have at least one parameter whose type is a class, enum, or reference to either, and the standard specifies initializer_list as a template class, so to me it seems like it should be conformant. However, apparently both Clang and GCC think I'm trying to use their non-standard block expressions.

GCC:

Compilation finished with errors:
source.cpp: In function 'int main()':
source.cpp:7:8: warning: left operand of comma operator has no effect [-Wunused-value]
source.cpp:7:9: error: expected ';' before '}' token
source.cpp:7:9: warning: right operand of comma operator has no effect [-Wunused-value]
source.cpp:7:13: error: expected primary-expression before '{' token
source.cpp:7:13: error: expected ';' before '{' token

Clang:

Compilation finished with errors:
source.cpp:7:5: warning: expression result unused [-Wunused-value]
   {1, 2} + {3, 4};
    ^
source.cpp:7:9: error: expected ';' after expression
   {1, 2} + {3, 4};
        ^
        ;
source.cpp:7:8: warning: expression result unused [-Wunused-value]
   {1, 2} + {3, 4};
       ^
source.cpp:7:13: error: expected expression
   {1, 2} + {3, 4};
            ^
2 warnings and 2 errors generated.

Should this compile? If not, why not?

EDIT:

And not surprisingly, the November CTP of VS 2012 fails as well:

error C2143: syntax error : missing ';' before '}'
error C2059: syntax error : '{'
error C2143: syntax error : missing ';' before '{'