Multiple changes...

- Makes use of empty Shape and empty Joint as is-destroyed info.
- Switches remaining IsDestroyed functions from using FindFree to using
  boolean is-destroyed info from Joint & Shape.
- Updates associated unit tests.

Library/include/playrho/d2/AabbTreeWorld.hpp

@@ -64,10 +64,13 @@
 #include <playrho/pmr/PoolMemoryResource.hpp>
 #include <playrho/pmr/StatsResource.hpp>
 
+#include <playrho/d2/Body.hpp>
 #include <playrho/d2/BodyConstraint.hpp>
 #include <playrho/d2/ContactImpulsesFunction.hpp>
 #include <playrho/d2/ContactManifoldFunction.hpp>
 #include <playrho/d2/DynamicTree.hpp>
+#include <playrho/d2/Joint.hpp>
+#include <playrho/d2/Shape.hpp>
 #include <playrho/d2/Transformation.hpp>
 #include <playrho/d2/WorldConf.hpp>
 
@@ -82,9 +85,6 @@ enum class BodyType;
 
 namespace playrho::d2 {
 
-class Body;
-class Joint;
-class Shape;
 class Manifold;
 class ContactImpulsesList;
 class AabbTreeWorld;
@@ -416,9 +416,12 @@ void SetJoint(AabbTreeWorld& world, JointID id, Joint def);
 void Destroy(AabbTreeWorld& world, JointID id);
 
 /// @brief Gets whether the given identifier is to a joint that's been destroyed.
-/// @note Complexity is at most O(n) where n is the number of elements free.
+/// @note Complexity is O(1).
 /// @see Destroy(AabbTreeWorld& world, JointID).
-bool IsDestroyed(const AabbTreeWorld& world, JointID id) noexcept;
+inline auto IsDestroyed(const AabbTreeWorld& world, JointID id) -> bool
+{
+    return IsDestroyed(GetJoint(world, id));
+}
 
 /// @}
 
@@ -466,9 +469,12 @@ void SetShape(AabbTreeWorld& world, ShapeID id, Shape def);
 void Destroy(AabbTreeWorld& world, ShapeID id);
 
 /// @brief Gets whether the given identifier is to a shape that's been destroyed.
-/// @note Complexity is at most O(n) where n is the number of elements free.
+/// @note Complexity is O(1).
 /// @see Destroy(AabbTreeWorld& world, ShapeID).
-bool IsDestroyed(const AabbTreeWorld& world, ShapeID id) noexcept;
+inline auto IsDestroyed(const AabbTreeWorld& world, ShapeID id) -> bool
+{
+    return IsDestroyed(GetShape(world, id));
+}
 
 /// @}
 
@@ -627,15 +633,13 @@ class AabbTreeWorld {
     friend const Joint& GetJoint(const AabbTreeWorld& world, JointID id);
     friend void SetJoint(AabbTreeWorld& world, JointID id, Joint def);
     friend void Destroy(AabbTreeWorld& world, JointID id);
-    friend bool IsDestroyed(const AabbTreeWorld& world, JointID id) noexcept;
 
     // Shape friend functions...
     friend ShapeCounter GetShapeRange(const AabbTreeWorld& world) noexcept;
     friend ShapeID CreateShape(AabbTreeWorld& world, Shape def);
     friend const Shape& GetShape(const AabbTreeWorld& world, ShapeID id);
     friend void SetShape(AabbTreeWorld& world, ShapeID id, Shape def);
     friend void Destroy(AabbTreeWorld& world, ShapeID id);
-    friend bool IsDestroyed(const AabbTreeWorld& world, ShapeID id) noexcept;
 
     // Contact friend functions...
     friend ContactCounter GetContactRange(const AabbTreeWorld& world) noexcept;

Library/include/playrho/d2/Joint.hpp

@@ -457,6 +457,13 @@ inline std::add_pointer_t<T> TypeCast(Joint* value) noexcept
     return nullptr;
 }
 
+/// @brief Gets whether the given entity is in the is-destroyed state.
+/// @relatedalso Joint
+inline auto IsDestroyed(const Joint &object) noexcept -> bool
+{
+    return !object.has_value();
+}
+
 /// Get the anchor point on body-A in local coordinates.
 /// @relatedalso Joint
 Length2 GetLocalAnchorA(const Joint& object);

Library/include/playrho/d2/Shape.hpp

@@ -497,6 +497,13 @@ inline T TypeCast(const Shape& value)
     return static_cast<T>(*tmp);
 }
 
+/// @brief Gets whether the given entity is in the is-destroyed state.
+/// @relatedalso Shape
+inline auto IsDestroyed(const Shape &value) noexcept -> bool
+{
+    return !value.has_value();
+}
+
 /// @brief Whether contact calculations should be performed between the two instances.
 /// @return <code>true</code> if contact calculations should be performed between these
 ///   two instances; <code>false</code> otherwise.

Library/source/playrho/d2/AabbTreeWorld.cpp

@@ -22,7 +22,6 @@
 #include <algorithm>
 #include <cassert> // for assert
 #include <cstddef> // for std::size_t
-#include <cstdint> // for std::uint32_t
 #include <exception> // for std::throw_with_nested
 #include <functional>
 #include <iterator> // for std::next
@@ -1112,14 +1111,17 @@ void SetJoint(AabbTreeWorld& world, JointID id, Joint def)
     }
     // Validate the references...
     auto &joint = At(world.m_jointBuffer, id, noSuchJointMsg);
+    if (!joint.has_value()) {
+        throw WasDestroyed{id, idIsDestroyedMsg};
+    }
     if (const auto bodyId = GetBodyA(def); bodyId != InvalidBodyID) {
         GetBody(world, bodyId);
     }
     if (const auto bodyId = GetBodyB(def); bodyId != InvalidBodyID) {
         GetBody(world, bodyId);
     }
-    if (world.m_jointBuffer.FindFree(to_underlying(id))) {
-        throw WasDestroyed{id, idIsDestroyedMsg};
+    if (!def.has_value()) {
+        throw WasDestroyed{def, "cannot be empty"};
     }
     world.Remove(id);
     joint = std::move(def);
@@ -1134,6 +1136,9 @@ JointID CreateJoint(AabbTreeWorld& world, Joint def)
     if (size(world.m_joints) >= MaxJoints) {
         throw LengthError("CreateJoint: operation would exceed MaxJoints");
     }
+    if (!def.has_value()) {
+        throw WasDestroyed{def, "cannot be empty"};
+    }
     // Validate the referenced bodies...
     if (const auto bodyId = GetBodyA(def); bodyId != InvalidBodyID) {
         GetBody(world, bodyId);
@@ -1220,18 +1225,16 @@ void Destroy(AabbTreeWorld& world, JointID id)
     }
 }
 
-bool IsDestroyed(const AabbTreeWorld& world, JointID id) noexcept
-{
-    return world.m_jointBuffer.FindFree(to_underlying(id));
-}
-
 ShapeCounter GetShapeRange(const AabbTreeWorld& world) noexcept
 {
     return static_cast<ShapeCounter>(size(world.m_shapeBuffer));
 }
 
 ShapeID CreateShape(AabbTreeWorld& world, Shape def)
 {
+    if (!def.has_value()) {
+        throw WasDestroyed{def, "cannot be empty"};
+    }
     const auto vertexRadius = GetVertexRadiusInterval(world);
     const auto childCount = GetChildCount(def);
     for (auto i = ChildCounter{0}; i < childCount; ++i) {
@@ -1272,11 +1275,6 @@ void Destroy(AabbTreeWorld& world, ShapeID id)
     world.m_shapeBuffer.Free(to_underlying(id));
 }
 
-bool IsDestroyed(const AabbTreeWorld& world, ShapeID id) noexcept
-{
-    return world.m_shapeBuffer.FindFree(to_underlying(id));
-}
-
 const Shape& GetShape(const AabbTreeWorld& world, ShapeID id)
 {
     return At(world.m_shapeBuffer, id, noSuchShapeMsg);
@@ -1288,9 +1286,12 @@ void SetShape(AabbTreeWorld& world, ShapeID id, Shape def) // NOLINT(readability
         throw WrongState(worldIsLockedMsg);
     }
     auto& shape = At(world.m_shapeBuffer, id, noSuchShapeMsg);
-    if (world.m_shapeBuffer.FindFree(to_underlying(id))) {
+    if (!shape.has_value()) {
         throw WasDestroyed{id, idIsDestroyedMsg};
     }
+    if (!def.has_value()) {
+        throw WasDestroyed{def, "cannot be empty"};
+    }
     const auto geometryChanged = IsGeomChanged(shape, def);
     for (auto&& b: world.m_bodyBuffer) {
         if (!Find(b.GetShapes(), id)) {

UnitTests/AabbTreeWorld.cpp

@@ -210,7 +210,7 @@ TEST(AabbTreeWorld, Clear)
     EXPECT_EQ(GetBodies(world).size(), std::size_t(0));
     EXPECT_EQ(GetJoints(world).size(), std::size_t(0));
     EXPECT_EQ(GetJointRange(world), 0u);
-    EXPECT_FALSE(IsDestroyed(world, JointID{0u})); // out-of-range so not destroyed
+    EXPECT_THROW(IsDestroyed(world, JointID{0u}), OutOfRange<JointID>);
 
     EXPECT_EQ(shapeListener.ids.size(), std::size_t(1));
 
@@ -1016,13 +1016,20 @@ TEST(AabbTreeWorld, AttachDetach)
     ASSERT_EQ(GetShapes(world, BodyID{0}).size(), 0u);
 }
 
-TEST(AabbTreeWorld, SetShapeThrowsWithOutOfRangeID)
+TEST(AabbTreeWorld, SetShapeThrowsWithEmpty)
 {
     auto world = AabbTreeWorld{};
     ASSERT_EQ(GetShapeRange(world), 0u);
     EXPECT_THROW(SetShape(world, ShapeID(0), Shape{}), OutOfRange<ShapeID>);
 }
 
+TEST(AabbTreeWorld, SetShapeThrowsWithOutOfRangeID)
+{
+    auto world = AabbTreeWorld{};
+    ASSERT_EQ(GetShapeRange(world), 0u);
+    EXPECT_THROW(SetShape(world, ShapeID(0), Shape{EdgeShapeConf{}}), OutOfRange<ShapeID>);
+}
+
 TEST(AabbTreeWorld, CreateBodyThrowsWithOutOfRangeShapeID)
 {
     auto world = AabbTreeWorld{};
@@ -1143,11 +1150,17 @@ TEST(AabbTreeWorld, SetShapeWithGeometryChange)
     EXPECT_EQ(size(GetProxies(world, bodyId)), 3u);
 }
 
-TEST(AabbTreeWorld, SetFreedShapeThrows)
+TEST(AabbTreeWorld, CreateEmptyShapeThrows)
+{
+    auto world = AabbTreeWorld{};
+    EXPECT_THROW(CreateShape(world, Shape()), WasDestroyed<Shape>);
+}
+
+TEST(AabbTreeWorld, SetDestroyedShapeThrows)
 {
     auto world = AabbTreeWorld{};
     auto id = InvalidShapeID;
-    ASSERT_NO_THROW(id = CreateShape(world, Shape()));
+    ASSERT_NO_THROW(id = CreateShape(world, Shape(EdgeShapeConf{})));
     ASSERT_NO_THROW(Destroy(world, id));
     ASSERT_TRUE(IsDestroyed(world, id));
     EXPECT_THROW(SetShape(world, id, Shape()), WasDestroyed<ShapeID>);
@@ -1162,15 +1175,29 @@ TEST(AabbTreeWorld, SetFreedBodyThrows)
     EXPECT_THROW(SetBody(world, id, Body()), WasDestroyed<BodyID>);
 }
 
-TEST(AabbTreeWorld, SetFreedJointThrows)
+TEST(AabbTreeWorld, CreateEmptyJointThrows)
+{
+    auto world = AabbTreeWorld{};
+    EXPECT_THROW(CreateJoint(world, Joint()), WasDestroyed<Joint>);
+}
+
+TEST(AabbTreeWorld, SetDestroyedJointThrows)
 {
     auto world = AabbTreeWorld{};
     auto id = InvalidJointID;
-    ASSERT_NO_THROW(id = CreateJoint(world, Joint()));
+    ASSERT_NO_THROW(id = CreateJoint(world, Joint(DistanceJointConf{})));
     ASSERT_NO_THROW(Destroy(world, id));
     EXPECT_THROW(SetJoint(world, id, Joint()), WasDestroyed<JointID>);
 }
 
+TEST(AabbTreeWorld, SetEmptyJointThrows)
+{
+    auto world = AabbTreeWorld{};
+    auto id = InvalidJointID;
+    ASSERT_NO_THROW(id = CreateJoint(world, Joint(DistanceJointConf{})));
+    EXPECT_THROW(SetJoint(world, id, Joint()), WasDestroyed<Joint>);
+}
+
 TEST(AabbTreeWorld, SetBodyWithShapeID)
 {
     auto world = AabbTreeWorld{};