/// Return true if the sequence [Begin, End) has exactly N items. Runs in O(N)
/// time. Not meant for use with random-access iterators.
-template <typename IterTy>
+/// Can optionally take a predicate to filter lazily some items.
+template<typename IterTy,
+ typename Pred = bool (*)(const decltype(*std::declval<IterTy>()) &)>
bool hasNItems(
IterTy &&Begin, IterTy &&End, unsigned N,
+ Pred &&ShouldBeCounted =
+ [](const decltype(*std::declval<IterTy>()) &) { return true; },
std::enable_if_t<
!std::is_same<typename std::iterator_traits<std::remove_reference_t<
decltype(Begin)>>::iterator_category,
std::random_access_iterator_tag>::value,
void> * = nullptr) {
- for (; N; --N, ++Begin)
+ for (; N; ++Begin) {
if (Begin == End)
return false; // Too few.
+ N -= ShouldBeCounted(*Begin);
+ }
return Begin == End;
}
/// Return true if the sequence [Begin, End) has N or more items. Runs in O(N)
/// time. Not meant for use with random-access iterators.
-template <typename IterTy>
+/// Can optionally take a predicate to filter lazily some items.
+template<typename IterTy,
+ typename Pred = bool (*)(const decltype(*std::declval<IterTy>()) &)>
bool hasNItemsOrMore(
IterTy &&Begin, IterTy &&End, unsigned N,
+ Pred &&ShouldBeCounted =
+ [](const decltype(*std::declval<IterTy>()) &) { return true; },
std::enable_if_t<
!std::is_same<typename std::iterator_traits<std::remove_reference_t<
decltype(Begin)>>::iterator_category,
std::random_access_iterator_tag>::value,
void> * = nullptr) {
- for (; N; --N, ++Begin)
+ for (; N; ++Begin) {
if (Begin == End)
return false; // Too few.
+ N -= ShouldBeCounted(*Begin);
+ }
return true;
}