only the registry should create views

src/entt/entity/view.hpp

@@ -13,6 +13,13 @@
 namespace entt {
 
 
+/**
+ * @brief Forward declaration of the registry class.
+ */
+template<typename>
+class Registry;
+
+
 /**
  * @brief Persistent view.
  *
@@ -56,12 +63,19 @@ template<typename Entity, typename... Component>
 class PersistentView final {
     static_assert(sizeof...(Component) > 1, "!");
 
+    /*! @brief A registry is allowed to create views. */
+    friend class Registry<Entity>;
+
     template<typename Comp>
     using pool_type = SparseSet<Entity, Comp>;
 
     using view_type = SparseSet<Entity>;
     using pattern_type = std::tuple<pool_type<Component> &...>;
 
+    PersistentView(view_type &view, pool_type<Component> &... pools) noexcept
+        : view{view}, pools{pools...}
+    {}
+
 public:
     /*! Input iterator type. */
     using iterator_type = typename view_type::iterator_type;
@@ -70,22 +84,6 @@ public:
     /*! @brief Unsigned integer type. */
     using size_type = typename view_type::size_type;
 
-    /**
-     * @brief Constructs a persistent view around a dedicated pool of entities.
-     *
-     * A persistent view is created out of:
-     *
-     * * A dedicated pool of entities that is shared between all the persistent
-     * views of the same type.
-     * * A bunch of pools of components to which to refer to get instances.
-     *
-     * @param view Shared reference to a dedicated pool of entities.
-     * @param pools References to pools of components.
-     */
-    PersistentView(view_type &view, pool_type<Component> &... pools) noexcept
-        : view{view}, pools{pools...}
-    {}
-
     /**
      * @brief Returns the number of entities that have the given components.
      * @return Number of entities that have the given components.
@@ -350,6 +348,9 @@ template<typename Entity, typename... Component>
 class View final {
     static_assert(sizeof...(Component) > 1, "!");
 
+    /*! @brief A registry is allowed to create views. */
+    friend class Registry<Entity>;
+
     template<typename Comp>
     using pool_type = SparseSet<Entity, Comp>;
 
@@ -413,6 +414,12 @@ class View final {
         underlying_iterator_type end;
     };
 
+    View(pool_type<Component> &... pools) noexcept
+        : pools{pools...}, view{nullptr}, unchecked{}
+    {
+        reset();
+    }
+
 public:
     /*! Input iterator type. */
     using iterator_type = Iterator;
@@ -421,16 +428,6 @@ public:
     /*! @brief Unsigned integer type. */
     using size_type = typename view_type::size_type;
 
-    /**
-     * @brief Constructs a view out of a bunch of pools of components.
-     * @param pools References to pools of components.
-     */
-    View(pool_type<Component> &... pools) noexcept
-        : pools{pools...}, view{nullptr}, unchecked{}
-    {
-        reset();
-    }
-
     /**
      * @brief Returns an iterator to the first entity that has the given
      * components.
@@ -677,8 +674,15 @@ private:
  */
 template<typename Entity, typename Component>
 class View<Entity, Component> final {
+    /*! @brief A registry is allowed to create views. */
+    friend class Registry<Entity>;
+
     using pool_type = SparseSet<Entity, Component>;
 
+    View(pool_type &pool) noexcept
+        : pool{pool}
+    {}
+
 public:
     /*! Input iterator type. */
     using iterator_type = typename pool_type::iterator_type;
@@ -689,14 +693,6 @@ public:
     /*! Type of the component iterated by the view. */
     using raw_type = typename pool_type::object_type;
 
-    /**
-     * @brief Constructs a view out of a pool of components.
-     * @param pool A reference to a pool of components.
-     */
-    View(pool_type &pool) noexcept
-        : pool{pool}
-    {}
-
     /**
      * @brief Returns the number of entities that have the given component.
      * @return Number of entities that have the given component.