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

Proposed resolution (February, 2012):

Change 7.7 [expr.const] paragraph 2 as follows:

• ...

• an lvalue-to-rvalue conversion (7.3.2 [conv.lval]) unless it is applied to

• a glvalue of integral or enumeration type that refers to a non-volatile const object with a preceding initialization, initialized with a constant expression, or

• a glvalue of literal type that refers to a non-volatile object defined with constexpr, or that refers to a non-mutable sub-object of such an object, or

• a glvalue of literal type that refers to a non-volatile temporary object whose lifetime has not ended, initialized with a constant expression;

• ...

Currently, literal class types can have mutable members. It is not clear whether that poses any particular problems with constexpr objects and constant expressions, and if so, what should be done about it.