From 18ffbd002720dcde328fa51b64ebd9ce69415ae2 Mon Sep 17 00:00:00 2001
From: Michele Caini <michele.caini@gmail.com>
Date: Mon, 4 Jan 2021 08:34:56 +0100
Subject: [PATCH] registry: group -> group_if_exists (close #626)

---
 src/entt/entity/helper.hpp   |  6 +++++-
 src/entt/entity/registry.hpp |  8 ++++----
 test/entt/entity/group.cpp   | 20 ++++++++++----------
 3 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/src/entt/entity/helper.hpp b/src/entt/entity/helper.hpp
index c8ee530b6..f65c8c960 100644
--- a/src/entt/entity/helper.hpp
+++ b/src/entt/entity/helper.hpp
@@ -89,7 +89,11 @@ struct as_group {
      */
     template<typename Exclude, typename Get, typename... Owned>
     operator basic_group<entity_type, Exclude, Get, Owned...>() const {
-        return reg.template group<Owned...>(Get{}, Exclude{});
+        if constexpr(std::is_const_v<registry_type>) {
+            return reg.template group_if_exists<Owned...>(Get{}, Exclude{});
+        } else {
+            return reg.template group<Owned...>(Get{}, Exclude{});
+        }
     }
 
 private:
diff --git a/src/entt/entity/registry.hpp b/src/entt/entity/registry.hpp
index 4a139027e..20bb0203c 100644
--- a/src/entt/entity/registry.hpp
+++ b/src/entt/entity/registry.hpp
@@ -1298,7 +1298,7 @@ public:
      * @return A newly created group.
      */
     template<typename... Owned, typename... Get, typename... Exclude>
-    [[nodiscard]] basic_group<Entity, exclude_t<Exclude...>, get_t<Get...>, Owned...> group(get_t<Get...>, exclude_t<Exclude...> = {}) const {
+    [[nodiscard]] basic_group<Entity, exclude_t<Exclude...>, get_t<Get...>, Owned...> group_if_exists(get_t<Get...>, exclude_t<Exclude...> = {}) const {
         static_assert(std::conjunction_v<std::is_const<Owned>..., std::is_const<Get>...>, "Invalid non-const type");
 
         if(auto it = std::find_if(groups.cbegin(), groups.cend(), [](const auto &gdata) {
@@ -1332,15 +1332,15 @@ public:
     /**
      * @brief Returns a group for the given components.
      *
-     * @sa group
+     * @sa group_if_exists
      *
      * @tparam Owned Types of components owned by the group.
      * @tparam Exclude Types of components used to filter the group.
      * @return A newly created group.
      */
     template<typename... Owned, typename... Exclude>
-    [[nodiscard]] basic_group<Entity, exclude_t<Exclude...>, get_t<>, Owned...> group(exclude_t<Exclude...> = {}) const {
-        return group<Owned...>(get_t<>{}, exclude<Exclude...>);
+    [[nodiscard]] basic_group<Entity, exclude_t<Exclude...>, get_t<>, Owned...> group_if_exists(exclude_t<Exclude...> = {}) const {
+        return group_if_exists<Owned...>(get_t<>{}, exclude<Exclude...>);
     }
 
     /**
diff --git a/test/entt/entity/group.cpp b/test/entt/entity/group.cpp
index 0a3be2c6c..5b18d7f54 100644
--- a/test/entt/entity/group.cpp
+++ b/test/entt/entity/group.cpp
@@ -16,7 +16,7 @@ bool operator==(const boxed_int &lhs, const boxed_int &rhs) {
 TEST(NonOwningGroup, Functionalities) {
     entt::registry registry;
     auto group = registry.group(entt::get<int, char>);
-    auto cgroup = std::as_const(registry).group(entt::get<const int, const char>);
+    auto cgroup = std::as_const(registry).group_if_exists(entt::get<const int, const char>);
 
     ASSERT_TRUE(group.empty());
 
@@ -79,7 +79,7 @@ TEST(NonOwningGroup, Functionalities) {
 
 TEST(NonOwningGroup, Invalid) {
     entt::registry registry{};
-    auto group = std::as_const(registry).group(entt::get<const empty_type, const int>);
+    auto group = std::as_const(registry).group_if_exists(entt::get<const empty_type, const int>);
 
     const auto entity = registry.create();
     registry.emplace<empty_type>(entity);
@@ -115,7 +115,7 @@ TEST(NonOwningGroup, Invalid) {
 TEST(NonOwningGroup, ElementAccess) {
     entt::registry registry;
     auto group = registry.group(entt::get<int, char>);
-    auto cgroup = std::as_const(registry).group(entt::get<const int, const char>);
+    auto cgroup = std::as_const(registry).group_if_exists(entt::get<const int, const char>);
 
     const auto e0 = registry.create();
     registry.emplace<int>(e0);
@@ -177,7 +177,7 @@ TEST(NonOwningGroup, Each) {
     registry.emplace<int>(e1, 1);
     registry.emplace<char>(e1);
 
-    auto cgroup = std::as_const(registry).group(entt::get<const int, const char>);
+    auto cgroup = std::as_const(registry).group_if_exists(entt::get<const int, const char>);
     std::size_t cnt = 0;
 
     for(auto first = cgroup.each().rbegin(), last = cgroup.each().rend(); first != last; ++first) {
@@ -487,7 +487,7 @@ TEST(NonOwningGroup, EmptyAndNonEmptyTypes) {
 TEST(NonOwningGroup, TrackEntitiesOnComponentDestruction) {
     entt::registry registry;
     const auto group = registry.group(entt::get<int>, entt::exclude<char>);
-    const auto cgroup = std::as_const(registry).group(entt::get<const int>, entt::exclude<char>);
+    const auto cgroup = std::as_const(registry).group_if_exists(entt::get<const int>, entt::exclude<char>);
 
     const auto entity = registry.create();
     registry.emplace<int>(entity);
@@ -591,7 +591,7 @@ TEST(NonOwningGroup, ExtendedGet) {
 TEST(OwningGroup, Functionalities) {
     entt::registry registry;
     auto group = registry.group<int>(entt::get<char>);
-    auto cgroup = std::as_const(registry).group<const int>(entt::get<const char>);
+    auto cgroup = std::as_const(registry).group_if_exists<const int>(entt::get<const char>);
 
     ASSERT_TRUE(group.empty());
 
@@ -652,7 +652,7 @@ TEST(OwningGroup, Functionalities) {
 
 TEST(OwningGroup, Invalid) {
     entt::registry registry{};
-    auto group = std::as_const(registry).group<const int>(entt::get<const empty_type>);
+    auto group = std::as_const(registry).group_if_exists<const int>(entt::get<const empty_type>);
 
     const auto entity = registry.create();
     registry.emplace<empty_type>(entity);
@@ -684,7 +684,7 @@ TEST(OwningGroup, Invalid) {
 TEST(OwningGroup, ElementAccess) {
     entt::registry registry;
     auto group = registry.group<int>(entt::get<char>);
-    auto cgroup = std::as_const(registry).group<const int>(entt::get<const char>);
+    auto cgroup = std::as_const(registry).group_if_exists<const int>(entt::get<const char>);
 
     const auto e0 = registry.create();
     registry.emplace<int>(e0);
@@ -746,7 +746,7 @@ TEST(OwningGroup, Each) {
     registry.emplace<int>(e1, 1);
     registry.emplace<char>(e1);
 
-    auto cgroup = std::as_const(registry).group<const int>(entt::get<const char>);
+    auto cgroup = std::as_const(registry).group_if_exists<const int>(entt::get<const char>);
     std::size_t cnt = 0;
 
     for(auto first = cgroup.each().rbegin(), last = cgroup.each().rend(); first != last; ++first) {
@@ -1160,7 +1160,7 @@ TEST(OwningGroup, EmptyAndNonEmptyTypes) {
 TEST(OwningGroup, TrackEntitiesOnComponentDestruction) {
     entt::registry registry;
     const auto group = registry.group<int>(entt::exclude<char>);
-    const auto cgroup = std::as_const(registry).group<const int>(entt::exclude<char>);
+    const auto cgroup = std::as_const(registry).group_if_exists<const int>(entt::exclude<char>);
 
     const auto entity = registry.create();
     registry.emplace<int>(entity);