+ /// placement delete - required by std, but never called.
+ void operator delete(void*, unsigned, bool) {
+ assert(0 && "Constructor throws?");
+ }
+protected:
+ template <int Idx, typename U> static Use &OpFrom(const U *that) {
+ return Idx < 0
+ ? OperandTraits<U>::op_end(const_cast<U*>(that))[Idx]
+ : OperandTraits<U>::op_begin(const_cast<U*>(that))[Idx];
+ }
+ template <int Idx> Use &Op() {
+ return OpFrom<Idx>(this);