c++ - Uniform initialization of references -

i trying understand new uniform initialization of c++0x. unfortunately, stumpled on using uniform initialization of references. example:

int main() {    int a;    int &ref{a}; } 

this example works fine:

% lang=c g++ uniform_init_of_ref.cpp -std=c++0x -o uni -wall -wextra uniform_init_of_ref.cpp: in function `int main()': uniform_init_of_ref.cpp:3:10: warning: unused variable `ref' [-wunused-variable] 

(update comeau throws error example, maybe gcc shouldn't compile well)

now, if use custom data type instead of integer, doesn't work anymore:

class y {};  int main() {     y y;     y &ref{y}; }  % lang=c g++ initialization.cpp -std=c++0x -o initialization -wall -wextra initialization.cpp: in function `int main()': initialization.cpp:9:13: error: invalid initialization of non-const reference of type `y&' rvalue of type `<brace-enclosed initializer list>' initialization.cpp:9:8: warning: unused variable `ref' [-wunused-variable] 

unfortunately, didn't find relevant section in standard draft. guess misunderstanding usage of uniform initialization, comeau complains message:

comeautest.c(9): error: reference variable "ref" requires initializer       y &ref{y}; 

so, can of point me in right direction?

---

in case want know why question relevant , why don't use y &ref(y): i'd able use uniform initialization in initialization list of constructor:

class x { };  class y {     const x& x;      public:         y (const x& xx):             x{xx}         {} };  int main () {     x x;     y y{x}; } 

this fails same error message above.

note:

• i using lang=c enable english error messages.
• gcc version: 4.6.1

according n2672 paragraph 8.5.4.4 should say:

otherwise, if t reference type, rvalue temporary of type referenced t list-initialized, , reference bound temporary. [ note: usual, binding fail , program ill-formed if reference type lvalue reference non-const type. ]

which (if understand correctly) means uniform initialization of references binds them new anonymous instances, seems me it's pretty useless. still not explain why 1 works , other not; should behave same (unless y has explicit constructors).