Re: Defeating (N)RVO
Daniel Kr?gler ha scritto:
#include <stdlib.h>
#include <algorithm>
#include <iostream>
template <typename RetType>
struct cheater {
private:
RetType value_;
int* refCnt_;
mutable bool hasRead_;
void swap(cheater& other) {
std::swap(value_, other.value_);
std::swap(refCnt_, other.refCnt_);
std::swap(hasRead_, other.hasRead_);
}
public:
cheater(RetType result) :
value_(result), refCnt_(new int(1)), hasRead_(false)
{
}
cheater(const cheater& src) :
value_(src.value_), refCnt_(src.refCnt_), hasRead_(src.hasRead_)
{
++*refCnt_;
}
cheater& operator=(const cheater& src)
{
cheater(src).swap(*this);
return *this;
}
~cheater()
{
if (--*refCnt_ == 0) {
delete refCnt_;
if (!hasRead_) {
abort();
}
}
}
operator RetType() const {
hasRead_ = true;
return value_;
}
};
I see a minor problem here. The hasRead_ state should be shared among
instances, otherwise even if I mark one copy as "inspected" the original
object would still remain "uninspected" and so it will throw if it
happens to be the last instance to be destroyed. I know that this case
won't happen in the typical use-case, but... who knows...
Ganesh
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