}
};
+namespace detail {
+/// Return a reference to the first or second member of a reference. Otherwise,
+/// return a copy of the member of a temporary.
+///
+/// When passing a range whose iterators return values instead of references,
+/// the reference must be dropped from `decltype((elt.first))`, which will
+/// always be a reference, to avoid returning a reference to a temporary.
+template <typename EltTy, typename FirstTy> class first_or_second_type {
+public:
+ using type =
+ typename std::conditional_t<std::is_reference<EltTy>::value, FirstTy,
+ std::remove_reference_t<FirstTy>>;
+};
+} // end namespace detail
+
/// Given a container of pairs, return a range over the first elements.
template <typename ContainerTy> auto make_first_range(ContainerTy &&c) {
- return llvm::map_range(
- std::forward<ContainerTy>(c),
- [](decltype((*std::begin(c))) elt) -> decltype((elt.first)) {
- return elt.first;
- });
+ using EltTy = decltype((*std::begin(c)));
+ return llvm::map_range(std::forward<ContainerTy>(c),
+ [](EltTy elt) -> typename detail::first_or_second_type<
+ EltTy, decltype((elt.first))>::type {
+ return elt.first;
+ });
}
/// Given a container of pairs, return a range over the second elements.
template <typename ContainerTy> auto make_second_range(ContainerTy &&c) {
+ using EltTy = decltype((*std::begin(c)));
return llvm::map_range(
std::forward<ContainerTy>(c),
- [](decltype((*std::begin(c))) elt) -> decltype((elt.second)) {
+ [](EltTy elt) ->
+ typename detail::first_or_second_type<EltTy,
+ decltype((elt.second))>::type {
return elt.second;
});
}