Merge pull request #180 from tcbrindle/pr/fix_cart_prod_last

Fix cartesian_product::last with empty sequence
tcbrindle · Mar 14, 2024 · 05c555e · 05c555e
2 parents 6719d90 + a25f209
commit 05c555e
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Showing 3 changed files with 44 additions and 3 deletions.
diff --git a/include/flux/op/cartesian_base.hpp b/include/flux/op/cartesian_base.hpp
@@ -270,9 +270,20 @@ struct cartesian_traits_base_impl {
     static constexpr auto last(Self& self) -> cursor_t<Self>
         requires cartesian_is_bounded<Bases...>
     {
-        auto cur = first(self);
-        std::get<0>(cur) = flux::last(get_base<0>(self));
-        return cur;
+        if constexpr (CartesianKind == cartesian_kind::product) {
+            auto cur = first(self);
+            bool any_is_empty = std::apply([](auto& /*ignored*/, auto&... bases) {
+                    return (flux::is_empty(bases) || ...);
+                }, self.bases_);
+            if (!any_is_empty) {
+                std::get<0>(cur) = flux::last(get_base<0>(self));
+            }
+            return cur;
+        } else {
+            auto cur = first(self);
+            std::get<0>(cur) = flux::last(get_base<0>(self));
+            return cur;
+        }
     }
 
     template <typename Self>

diff --git a/test/test_cartesian_power.cpp b/test/test_cartesian_power.cpp
@@ -261,9 +261,24 @@ constexpr bool test_cartesian_power()
 
 static_assert(test_cartesian_power());
 
+// https://github.com/tcbrindle/flux/issues/177
+constexpr bool issue_177()
+{
+    auto seq = flux::cartesian_power<3>(flux::empty<int>);
+
+    STATIC_CHECK(seq.is_empty());
+    STATIC_CHECK(seq.size() == 0);
+    STATIC_CHECK(seq.is_last(seq.first()));
+    STATIC_CHECK(seq.first() == seq.last());
+
+    return true;
+}
+static_assert(issue_177());
+
 }
 
 TEST_CASE("cartesian power")
 {
     REQUIRE(test_cartesian_power());
+    REQUIRE(issue_177());
 }
diff --git a/test/test_cartesian_product.cpp b/test/test_cartesian_product.cpp
@@ -509,11 +509,26 @@ void issue_167()
     REQUIRE_THROWS_AS(flux::size(prod), flux::unrecoverable_error);
 }
 
+// https://github.com/tcbrindle/flux/issues/177
+constexpr bool issue_177()
+{
+    auto seq = flux::cartesian_product(std::array{1, 2, 3}, flux::empty<int>);
+
+    STATIC_CHECK(seq.is_empty());
+    STATIC_CHECK(seq.size() == 0);
+    STATIC_CHECK(seq.is_last(seq.first()));
+    STATIC_CHECK(seq.first() == seq.last());
+
+    return true;
+}
+static_assert(issue_177());
+
 }
 
 TEST_CASE("cartesian_product")
 {
     REQUIRE(test_cartesian_product());
 
     issue_167();
+    REQUIRE(issue_177());
 }