[Moved to DR at the April, 2013 meeting.]

Proposed resolution (August, 2012):

Change 7.6.19 [expr.ass] paragraph 9 as follows:

A braced-init-list may appear on the right-hand side of

• an assignment to a scalar, in which case the initializer list shall have at most a single element. The meaning of x={v}, where T is the scalar type of the expression x, is that of x=T(v) except that no narrowing conversion (8.5.4) is allowed. The meaning of x={} is x=T().

• an assignment defined by a user-defined assignment operator to an object of class type, in which case the initializer list is passed as the argument to the assignment operator function selected by overload resolution (12.4.3.2 [over.ass], 12.2 [over.match]).

According to 7.6.19 [expr.ass] paragraph 9,

A braced-init-list may appear on the right-hand side of

• an assignment to a scalar...

• an assignment defined by a user-defined assignment operator, in which case the initializer list is passed as the argument to the operator function.

Presumably the phrase “user-defined” is not intended to forbid an example like

  struct A {
    A();
    A ( std::initializer_list<int> ) ;
  };
  void f() {
    A a;
    a = {37};
  }

which relies on an implicitly-declared assignment operator.