[topology] have Neighbor/Child/Router inherit from InstanceLocatorInit (#4569)

This commit changes the `Neighbor` class (and therefore its sub-classes
`Child` and `Router`) to inherit from `InstanceLoatorInit`. It adds
`Init()` method to them as well and ensures that they are initialized
before use from `ChildTable`, `RouterTable` and `Mle` classes.

src/core/thread/child_table.cpp

@@ -102,7 +102,11 @@ ChildTable::ChildTable(Instance &aInstance)
     : InstanceLocator(aInstance)
     , mMaxChildrenAllowed(kMaxChildren)
 {
-    Clear();
+    for (Child *child = &mChildren[0]; child < OT_ARRAY_END(mChildren); child++)
+    {
+        child->Init(aInstance);
+        child->Clear();
+    }
 }
 
 void ChildTable::Clear(void)

src/core/thread/mle.cpp

@@ -114,6 +114,9 @@ Mle::Mle(Instance &aInstance)
 {
     otMeshLocalPrefix meshLocalPrefix;
 
+    mParent.Init(aInstance);
+    mParentCandidate.Init(aInstance);
+
     mLeaderData.Clear();
     mParentLeaderData.Clear();
     mParent.Clear();

src/core/thread/router_table.cpp

@@ -65,6 +65,11 @@ RouterTable::RouterTable(Instance &aInstance)
     , mRouterIdSequence(Random::NonCrypto::GetUint8())
     , mActiveRouterCount(0)
 {
+    for (uint8_t index = 0; index < Mle::kMaxRouters; index++)
+    {
+        mRouters[index].Init(aInstance);
+    }
+
     Clear();
 }
 

src/core/thread/topology.cpp

@@ -41,6 +41,12 @@
 
 namespace ot {
 
+void Neighbor::Init(Instance &aInstance)
+{
+    InstanceLocatorInit::Init(aInstance);
+    SetState(kStateInvalid);
+}
+
 bool Neighbor::IsStateValidOrAttaching(void) const
 {
     bool rval = false;
@@ -105,8 +111,10 @@ void Neighbor::GenerateChallenge(void)
 
 void Child::Clear(void)
 {
+    Instance &instance = GetInstance();
+
     memset(reinterpret_cast<void *>(this), 0, sizeof(Child));
-    SetState(kStateInvalid);
+    Init(instance);
 }
 
 void Child::ClearIp6Addresses(void)
@@ -282,8 +290,10 @@ void Child::GenerateChallenge(void)
 
 void Router::Clear(void)
 {
+    Instance &instance = GetInstance();
+
     memset(reinterpret_cast<void *>(this), 0, sizeof(Router));
-    SetState(kStateInvalid);
+    Init(instance);
 }
 
 } // namespace ot

src/core/thread/topology.hpp

@@ -38,6 +38,7 @@
 
 #include <openthread/thread_ftd.h>
 
+#include "common/locator.hpp"
 #include "common/message.hpp"
 #include "common/random.hpp"
 #include "common/timer.hpp"
@@ -50,13 +51,11 @@
 
 namespace ot {
 
-class Instance;
-
 /**
  * This class represents a Thread neighbor.
  *
  */
-class Neighbor
+class Neighbor : public InstanceLocatorInit
 {
 public:
     /**
@@ -420,6 +419,15 @@ public:
     void SetTimeSyncEnabled(bool aEnabled) { mTimeSyncEnabled = aEnabled; }
 #endif
 
+protected:
+    /**
+     * This method initializes the `Neighbor` object.
+     *
+     * @param[in] aInstance  A reference to OpenThread instance.
+     *
+     */
+    void Init(Instance &aInstance);
+
 private:
     Mac::ExtAddress mMacAddr;   ///< The IEEE 802.15.4 Extended Address
     TimeMilli       mLastHeard; ///< Time when last heard.
@@ -511,6 +519,14 @@ public:
         otChildIp6AddressIterator mIndex;
     };
 
+    /**
+     * This method initializes the `Child` object.
+     *
+     * @param[in] aInstance  A reference to OpenThread instance.
+     *
+     */
+    void Init(Instance &aInstance) { Neighbor::Init(aInstance); }
+
     /**
      * This method clears the child entry.
      *
@@ -726,6 +742,14 @@ private:
 class Router : public Neighbor
 {
 public:
+    /**
+     * This method initializes the `Router` object.
+     *
+     * @param[in] aInstance  A reference to OpenThread instance.
+     *
+     */
+    void Init(Instance &aInstance) { Neighbor::Init(aInstance); }
+
     /**
      * This method clears the router entry.
      *

tests/unit/test_child.cpp

@@ -120,6 +120,8 @@ void TestChildIp6Address(void)
     sInstance = testInitInstance();
     VerifyOrQuit(sInstance != NULL, "Null instance");
 
+    child.Init(*sInstance);
+
     //- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 
     printf("\nConverting IPv6 addresses from string");