Use of destructed object in lager::lenses::getset #160
Description
Hi!
I have found a weird issue in lager::lenses::getset. It looks like both lambdas accept std::forward<decltype(p)>(p), which causes the object to be moved twice. To make this happen, both getter and setter functions should accept a normal object, not a reference.
template <typename Getter, typename Setter>
auto getset(Getter&& getter, Setter&& setter)
{
return zug::comp([=](auto&& f) {
return [&, f = LAGER_FWD(f)](auto&& p) {
// here we call a move constructor for decltype(p) and besically expire p
return f(getter(std::forward<decltype(p)>(p)))([&](auto&& x) {
// here we try to do that again, while the object has already been expired
return setter(std::forward<decltype(p)>(p),
std::forward<decltype(x)>(x));
});
};
});
}Example code:
struct Data : public boost::equality_comparable<Data>
{
QString id = "default_id";
QString curve = "default_value";
Data() = default;
Data(const Data&) = default;
Data(Data&&) = default;
Data& operator=(const Data&) = default;
Data& operator=(Data&&) = default;
bool operator==(const Data&rhs) { return id == rhs.id && curve == rhs.curve; }
};
auto testCurveLensNoTuple = lager::lenses::getset(
[](Data data) -> QString {
qDebug() << "get" << data.curve;
return data.curve;
},
[](Data data, QString curve) {
qDebug() << "set" << data.curve << data.id;
Q_ASSERT(!data.curve.isEmpty());
data.curve = curve;
return data;
});
void test()
{
lager::state<Data, lager::automatic_tag> state;
// this line asserts!
lager::cursor<QString> activeCurve = state.zoom(testCurveLensNoTuple);
// this line works fine
// lager::cursor<QString> activeCurve = state.zoom(lager::lenses::attr(&Data::curve));
qDebug() << ppVar(activeCurve.get()) << ppVar(state->curve) << ppVar(state->id);
activeCurve.set(DEFAULT_CURVE_STRING);
qDebug() << ppVar(activeCurve.get()) << ppVar(state->curve) << ppVar(state->id);
}
I'm not sure what is the best way to fix that. The simplest solution could be to make a copy of the object in lager::lenses::getset, which doesn't look like the best solution. Perhaps it is possible to implement getset routine without lambdas and avoud this extra copy?