From 6b95c614bb63d25ea35f95d48473c7e5f82c66fb Mon Sep 17 00:00:00 2001
From: Michele Caini <michele.caini@gmail.com>
Date: Fri, 21 Feb 2025 12:36:03 +0100
Subject: [PATCH] view: setup placeholders on view packs - close #1224

---
 src/entt/entity/view.hpp  |  5 +++--
 test/entt/entity/view.cpp | 28 +++++++++++++++++++++++++++-
 2 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/src/entt/entity/view.hpp b/src/entt/entity/view.hpp
index 07e0dda62..42cc77ad1 100644
--- a/src/entt/entity/view.hpp
+++ b/src/entt/entity/view.hpp
@@ -52,7 +52,8 @@ template<typename Result, typename View, typename Other, std::size_t... GLhs, st
     Result elem{};
     // friend-initialization, avoid multiple calls to refresh
     elem.pools = {view.template storage<GLhs>()..., other.template storage<GRhs>()...};
-    elem.filter = {view.template storage<sizeof...(GLhs) + ELhs>()..., other.template storage<sizeof...(GRhs) + ERhs>()...};
+    auto filter_or_placeholder = [placeholder = elem.placeholder](auto *value) { return (value == nullptr) ? placeholder : value; };
+    elem.filter = {filter_or_placeholder(view.template storage<sizeof...(GLhs) + ELhs>())..., filter_or_placeholder(other.template storage<sizeof...(GRhs) + ERhs>())...};
     elem.refresh();
     return elem;
 }
@@ -255,7 +256,7 @@ class basic_common_view {
 protected:
     /*! @cond TURN_OFF_DOXYGEN */
     basic_common_view() noexcept {
-        for(size_type pos{}; pos < Exclude; ++pos) {
+        for(size_type pos{}, last = filter.size(); pos < last; ++pos) {
             filter[pos] = placeholder;
         }
     }
diff --git a/test/entt/entity/view.cpp b/test/entt/entity/view.cpp
index 69cf86667..db187c56a 100644
--- a/test/entt/entity/view.cpp
+++ b/test/entt/entity/view.cpp
@@ -1393,7 +1393,7 @@ TEST(MultiStorageView, Storage) {
 
 TEST(MultiStorageView, SwapStorage) {
     std::tuple<entt::storage<int>, entt::storage<char>, entt::storage<int>, entt::storage<char>> storage{};
-    entt::basic_view<entt::get_t<entt::storage<int>>, entt::exclude_t<const entt::storage<char>>> view;
+    entt::basic_view<entt::get_t<entt::storage<int>>, entt::exclude_t<const entt::storage<char>>> view{};
     const entt::entity entity{0};
 
     ASSERT_FALSE(view);
@@ -1583,3 +1583,29 @@ TEST(View, Pipe) {
     ASSERT_NE(pack32.storage<const int>(), nullptr);
     ASSERT_NE(pack32.storage<float>(), nullptr);
 }
+
+TEST(View, PipeWithPlaceholder) {
+    entt::storage<void> storage{};
+    const entt::entity entity{0};
+
+    const entt::basic_view view{storage};
+    entt::basic_view<entt::get_t<entt::storage<void>>, entt::exclude_t<entt::storage<int>>> other{};
+
+    other.storage(storage);
+
+    ASSERT_FALSE(view.contains(entity));
+    ASSERT_FALSE(other.contains(entity));
+
+    auto pack = view | other;
+
+    ASSERT_FALSE(pack.contains(entity));
+
+    storage.emplace(entity);
+
+    ASSERT_TRUE(view.contains(entity));
+    ASSERT_TRUE(other.contains(entity));
+
+    pack = view | other;
+
+    ASSERT_TRUE(pack.contains(entity));
+}