http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48450
Summary: [C++0x][SFINAE] Hard errors with static_cast
expressions
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: daniel.krueg...@googlemail.com
CC: ja...@redhat.com
The following families of expressions give hard compiler errors in a SFINAE
context:
a) any T => abstract class
b) cv void* => T* (T != void)
c) cv Base* => Derived*
d) cv T Derived::* => T Base::*
e) cv void => T (T is a class type)
f) Scoped enum => bool
The following code should be well-formed, but is not:
#include <utility> // for declval
template<class To, class From,
class = decltype(static_cast<To>(std::declval<From>()))
>
char f(int);
template<class, class>
char (&f(...))[2];
struct A { virtual ~A() = 0; };
struct B {};
struct D : B {};
enum class SE {};
static_assert(sizeof(f<A, int>(0)) != 1, "Error"); // a
static_assert(sizeof(f<int*, const void*>(0)) != 1, "Error"); // b
static_assert(sizeof(f<D*, const B*>(0)) != 1, "Error"); // c
static_assert(sizeof(f<int B::*, const int D::*>(0)) != 1, "Error"); // d
static_assert(sizeof(f<B, void>(0)) != 1, "Error"); // e
static_assert(sizeof(f<bool, SE>(0)) == 1, "Error"); // f
a) "error: cannot allocate an object of abstract type 'A' because the
following virtual functions are pure within 'A': virtual A::~A()"
b) "error: static_cast from type 'const void*' to type 'int*' casts
away qualifiers"
c) "error: static_cast from type 'const B*' to type 'D*' casts away qualifiers"
d) "error: static_cast from type 'const int D::*' to type 'int B::*'
casts away qualifiers"
e) "error: invalid use of void expression"
f) "error: invalid operands of types 'SE' and 'int' to binary 'operator!='"
