Contextual implicit conversion

cic.cpp

# https://groups.google.com/a/isocpp.org/forum/#!topic/std-discussion/rvbQiAx38Tg%5B1-25-false%5D
# http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3323.pdf

struct C1 { enum class A{}; operator A(); explicit operator unsigned(); } c1;
struct C2 { operator char*(); explicit operator bool(); } c2;
struct C3 { operator int() = delete; operator unsigned(); } c3;
struct C4 { explicit operator int() = delete; operator unsigned(); } c4;
struct C5 { operator int(); explicit operator unsigned(); } c5;
void f() {
  switch (c1) {}
  switch (c2) {}
  switch (c3) {}
  switch (c4) {}
  switch (c5) {}
}