[child-table] enable use of range-based "for" loop (#5239)

This commit updates `ChildTable` class. It mainly adds support for
using range-based `for` loops to iterate over all child entries
(matching a given state filter). It also simplifies the `Iterator`
implementation (removing the now unused behavior to start the
iteration from a specific child in the table). The unit test
`test_child_table` is also updated to add tests for the newly added
behavior.

src/core/mac/data_poll_handler.cpp

@@ -79,9 +79,8 @@ DataPollHandler::DataPollHandler(Instance &aInstance)
 
 void DataPollHandler::Clear(void)
 {
-    for (ChildTable::Iterator iter(GetInstance(), Child::kInStateAnyExceptInvalid); !iter.IsDone(); iter++)
+    for (Child &child : Get<ChildTable>().Iterate(Child::kInStateAnyExceptInvalid))
     {
-        Child &child = *iter.GetChild();
         child.SetDataPollPending(false);
         child.SetFrameReplacePending(false);
         child.SetFramePurgePending(false);
@@ -289,20 +288,18 @@ exit:
 
 void DataPollHandler::ProcessPendingPolls(void)
 {
-    for (ChildTable::Iterator iter(GetInstance(), Child::kInStateValidOrRestoring); !iter.IsDone(); iter++)
+    for (Child &child : Get<ChildTable>().Iterate(Child::kInStateValidOrRestoring))
     {
-        Child *child = iter.GetChild();
-
-        if (!child->IsDataPollPending())
+        if (!child.IsDataPollPending())
         {
             continue;
         }
 
         // Find the child with earliest poll receive time.
 
-        if ((mIndirectTxChild == nullptr) || (child->GetLastHeard() < mIndirectTxChild->GetLastHeard()))
+        if ((mIndirectTxChild == nullptr) || (child.GetLastHeard() < mIndirectTxChild->GetLastHeard()))
         {
-            mIndirectTxChild = child;
+            mIndirectTxChild = &child;
         }
     }
 

src/core/thread/address_resolver.cpp

@@ -723,10 +723,8 @@ void AddressResolver::HandleAddressError(Coap::Message &aMessage, const Ip6::Mes
 
     meshLocalIid.ConvertToExtAddress(extAddr);
 
-    for (ChildTable::Iterator iter(GetInstance(), Child::kInStateValid); !iter.IsDone(); iter++)
+    for (Child &child : Get<ChildTable>().Iterate(Child::kInStateValid))
     {
-        Child &child = *iter.GetChild();
-
         if (child.IsFullThreadDevice())
         {
             continue;
@@ -780,10 +778,8 @@ void AddressResolver::HandleAddressQuery(Coap::Message &aMessage, const Ip6::Mes
         ExitNow();
     }
 
-    for (ChildTable::Iterator iter(GetInstance(), Child::kInStateValid); !iter.IsDone(); iter++)
+    for (Child &child : Get<ChildTable>().Iterate(Child::kInStateValid))
     {
-        Child &child = *iter.GetChild();
-
         if (child.IsFullThreadDevice() || child.GetLinkFailures() >= Mle::kFailedChildTransmissions)
         {
             continue;

src/core/thread/child_table.cpp

@@ -44,16 +44,6 @@ namespace ot {
 ChildTable::Iterator::Iterator(Instance &aInstance, Child::StateFilter aFilter)
     : InstanceLocator(aInstance)
     , mFilter(aFilter)
-    , mStart(nullptr)
-    , mChild(nullptr)
-{
-    Reset();
-}
-
-ChildTable::Iterator::Iterator(Instance &aInstance, Child::StateFilter aFilter, Child *aStartingChild)
-    : InstanceLocator(aInstance)
-    , mFilter(aFilter)
-    , mStart(aStartingChild)
     , mChild(nullptr)
 {
     Reset();
@@ -61,12 +51,7 @@ ChildTable::Iterator::Iterator(Instance &aInstance, Child::StateFilter aFilter,
 
 void ChildTable::Iterator::Reset(void)
 {
-    if (mStart == nullptr)
-    {
-        mStart = &Get<ChildTable>().mChildren[0];
-    }
-
-    mChild = mStart;
+    mChild = &Get<ChildTable>().mChildren[0];
 
     if (!mChild->MatchesFilter(mFilter))
     {
@@ -76,22 +61,12 @@ void ChildTable::Iterator::Reset(void)
 
 void ChildTable::Iterator::Advance(void)
 {
-    ChildTable &childTable = Get<ChildTable>();
-    Child *     listStart  = &childTable.mChildren[0];
-    Child *     listEnd    = &childTable.mChildren[childTable.mMaxChildrenAllowed];
-
     VerifyOrExit(mChild != nullptr, OT_NOOP);
 
     do
     {
         mChild++;
-
-        if (mChild >= listEnd)
-        {
-            mChild = listStart;
-        }
-
-        VerifyOrExit(mChild != mStart, mChild = nullptr);
+        VerifyOrExit(mChild < &Get<ChildTable>().mChildren[Get<ChildTable>().mMaxChildrenAllowed], mChild = nullptr);
     } while (!mChild->MatchesFilter(mFilter));
 
 exit:

src/core/thread/child_table.hpp

@@ -49,6 +49,8 @@ namespace ot {
  */
 class ChildTable : public InstanceLocator
 {
+    class IteratorBuilder;
+
 public:
     /**
      * This class represents an iterator for iterating through the child entries in the child table.
@@ -56,9 +58,11 @@ public:
      */
     class Iterator : public InstanceLocator
     {
+        friend class IteratorBuilder;
+
     public:
         /**
-         * This constructor initializes an `Iterator` instance to start from beginning of the child table.
+         * This constructor initializes an `Iterator` instance.
          *
          * @param[in] aInstance  A reference to the OpenThread instance.
          * @param[in] aFilter    A child state filter.
@@ -66,23 +70,6 @@ public:
          */
         Iterator(Instance &aInstance, Child::StateFilter aFilter);
 
-        /**
-         * This constructor initializes an `Iterator` instance to start from a given child.
-         *
-         * This constructor allows the iterator to start from a given `Child` entry. The iterator will start from the
-         * given child and will go through all entries in the child table (matching the filter) till it gets back to
-         * the starting `Child` entry.
-         *
-         * If the given starting `Child` pointer is `nullptr`, then the iterator starts from beginning of the child
-         * table.
-         *
-         * @param[in] aInstance        A reference to the OpenThread instance.
-         * @param[in] aFilter          A child state filter.
-         * @param[in] aStartingChild   A pointer to a child. If non-nullptr, the iterator starts from the given entry.
-         *
-         */
-        Iterator(Instance &aInstance, Child::StateFilter aFilter, Child *aStartingChild);
-
         /**
          * This method resets the iterator to start over.
          *
@@ -99,16 +86,6 @@ public:
          */
         bool IsDone(void) const { return (mChild == nullptr); }
 
-        /**
-         * This method advances the iterator.
-         *
-         * The iterator is moved to point to the next `Child` entry matching the given state filter in the constructor.
-         * If there are no more `Child` entries matching the given filter, the iterator becomes empty (i.e.,
-         * `GetChild()` returns `nullptr` and `IsDone()` returns `true`).
-         *
-         */
-        void Advance(void);
-
         /**
          * This method overloads `++` operator (pre-increment) to advance the iterator.
          *
@@ -137,9 +114,61 @@ public:
          */
         Child *GetChild(void) { return mChild; }
 
+        /**
+         * This method overloads the `*` dereference operator and gets a reference to `Child` entry to which the
+         * iterator is currently pointing.
+         *
+         * This method MUST be used when the iterator is not empty/finished (i.e., `IsDone()` returns `false`).
+         *
+         * @returns A reference to the `Child` entry currently pointed by the iterator.
+         *
+         */
+        Child &operator*(void) { return *mChild; }
+
+        /**
+         * This method overloads the `->` dereference operator and gets a pointer to `Child` entry to which the iterator
+         * is currently pointing.
+         *
+         * @returns A pointer to the `Child` entry associated with the iterator, or `nullptr` if iterator is empty/done.
+         *
+         */
+        Child *operator->(void) { return mChild; }
+
+        /**
+         * This method overloads operator `==` to evaluate whether or not two `Iterator` instances point to the same
+         * child entry.
+         *
+         * @param[in]  aOther  The other `Iterator` to compare with.
+         *
+         * @retval TRUE   If the two `Iterator` objects point to the same child entry or both are done.
+         * @retval FALSE  If the two `Iterator` objects do not point to the same child entry.
+         *
+         */
+        bool operator==(const Iterator &aOther) const { return mChild == aOther.mChild; }
+
+        /**
+         * This method overloads operator `!=` to evaluate whether or not two `Iterator` instances point to the same
+         * child entry.
+         *
+         * @param[in]  aOther  The other `Iterator` to compare with.
+         *
+         * @retval TRUE   If the two `Iterator` objects do not point to the same child entry.
+         * @retval FALSE  If the two `Iterator` objects point to the same child entry or both are done.
+         *
+         */
+        bool operator!=(const Iterator &aOther) const { return mChild != aOther.mChild; }
+
     private:
+        Iterator(Instance &aInstance)
+            : InstanceLocator(aInstance)
+            , mFilter(Child::StateFilter::kInStateValid)
+            , mChild(nullptr)
+        {
+        }
+
+        void Advance(void);
+
         Child::StateFilter mFilter;
-        Child *            mStart;
         Child *            mChild;
     };
 
@@ -276,12 +305,43 @@ public:
      */
     otError SetMaxChildrenAllowed(uint16_t aMaxChildren);
 
+    /**
+     * This method enables range-based `for` loop iteration over all child entries in the child table matching a given
+     * state filter.
+     *
+     * This method should be used as follows:
+     *
+     *     for (Child &child : aChildTable.Iterate(aFilter)) { ... }
+     *
+     * @param[in] aFilter  A child state filter.
+     *
+     * @returns An IteratorBuilder instance.
+     *
+     */
+    IteratorBuilder Iterate(Child::StateFilter aFilter) { return IteratorBuilder(GetInstance(), aFilter); }
+
 private:
     enum
     {
         kMaxChildren = OPENTHREAD_CONFIG_MLE_MAX_CHILDREN,
     };
 
+    class IteratorBuilder : public InstanceLocator
+    {
+    public:
+        IteratorBuilder(Instance &aInstance, Child::StateFilter aFilter)
+            : InstanceLocator(aInstance)
+            , mFilter(aFilter)
+        {
+        }
+
+        Iterator begin(void) { return Iterator(GetInstance(), mFilter); }
+        Iterator end(void) { return Iterator(GetInstance()); }
+
+    private:
+        Child::StateFilter mFilter;
+    };
+
     uint16_t mMaxChildrenAllowed;
     Child    mChildren[kMaxChildren];
 };

src/core/thread/indirect_sender.cpp

@@ -72,10 +72,10 @@ void IndirectSender::Stop(void)
 {
     VerifyOrExit(mEnabled, OT_NOOP);
 
-    for (ChildTable::Iterator iter(GetInstance(), Child::kInStateAnyExceptInvalid); !iter.IsDone(); iter++)
+    for (Child &child : Get<ChildTable>().Iterate(Child::kInStateAnyExceptInvalid))
     {
-        iter.GetChild()->SetIndirectMessage(nullptr);
-        mSourceMatchController.ResetMessageCount(*iter.GetChild());
+        child.SetIndirectMessage(nullptr);
+        mSourceMatchController.ResetMessageCount(child);
     }
 
     mDataPollHandler.Clear();
@@ -556,14 +556,14 @@ exit:
 
 void IndirectSender::ClearMessagesForRemovedChildren(void)
 {
-    for (ChildTable::Iterator iter(GetInstance(), Child::kInStateAnyExceptValidOrRestoring); !iter.IsDone(); iter++)
+    for (Child &child : Get<ChildTable>().Iterate(Child::kInStateAnyExceptValidOrRestoring))
     {
-        if (iter.GetChild()->GetIndirectMessageCount() == 0)
+        if (child.GetIndirectMessageCount() == 0)
         {
             continue;
         }
 
-        ClearAllMessagesForSleepyChild(*iter.GetChild());
+        ClearAllMessagesForSleepyChild(child);
     }
 }
 

src/core/thread/key_manager.cpp

@@ -130,11 +130,11 @@ otError KeyManager::SetMasterKey(const MasterKey &aKey)
     }
 
     // reset child frame counters
-    for (ChildTable::Iterator iter(GetInstance(), Child::kInStateAnyExceptInvalid); !iter.IsDone(); iter++)
+    for (Child &child : Get<ChildTable>().Iterate(Child::kInStateAnyExceptInvalid))
     {
-        iter.GetChild()->SetKeySequence(0);
-        iter.GetChild()->SetLinkFrameCounter(0);
-        iter.GetChild()->SetMleFrameCounter(0);
+        child.SetKeySequence(0);
+        child.SetLinkFrameCounter(0);
+        child.SetMleFrameCounter(0);
     }
 #endif
 

src/core/thread/mesh_forwarder.cpp

@@ -138,9 +138,9 @@ void MeshForwarder::RemoveMessage(Message &aMessage)
     if (queue == &mSendQueue)
     {
 #if OPENTHREAD_FTD
-        for (ChildTable::Iterator iter(GetInstance(), Child::kInStateAnyExceptInvalid); !iter.IsDone(); iter++)
+        for (Child &child : Get<ChildTable>().Iterate(Child::kInStateAnyExceptInvalid))
         {
-            IgnoreError(mIndirectSender.RemoveMessageFromSleepyChild(aMessage, *iter.GetChild()));
+            IgnoreError(mIndirectSender.RemoveMessageFromSleepyChild(aMessage, child));
         }
 #endif
 

src/core/thread/mesh_forwarder_ftd.cpp

@@ -80,11 +80,8 @@ otError MeshForwarder::SendMessage(Message &aMessage)
                     ip6Header.GetDestination() == mle.GetRealmLocalAllThreadNodesAddress())
                 {
                     // destined for all sleepy children
-                    for (ChildTable::Iterator iter(GetInstance(), Child::kInStateValidOrRestoring); !iter.IsDone();
-                         iter++)
+                    for (Child &child : Get<ChildTable>().Iterate(Child::kInStateValidOrRestoring))
                     {
-                        Child &child = *iter.GetChild();
-
                         if (!child.IsRxOnWhenIdle())
                         {
                             mIndirectSender.AddMessageForSleepyChild(aMessage, child);
@@ -94,11 +91,8 @@ otError MeshForwarder::SendMessage(Message &aMessage)
                 else
                 {
                     // destined for some sleepy children which subscribed the multicast address.
-                    for (ChildTable::Iterator iter(GetInstance(), Child::kInStateValidOrRestoring); !iter.IsDone();
-                         iter++)
+                    for (Child &child : Get<ChildTable>().Iterate(Child::kInStateValidOrRestoring))
                     {
-                        Child &child = *iter.GetChild();
-
                         if (mle.IsSleepyChildSubscribed(ip6Header.GetDestination(), child))
                         {
                             mIndirectSender.AddMessageForSleepyChild(aMessage, child);
@@ -329,9 +323,9 @@ void MeshForwarder::RemoveDataResponseMessages(void)
 
         if (!(ip6Header.GetDestination().IsMulticast()))
         {
-            for (ChildTable::Iterator iter(GetInstance(), Child::kInStateAnyExceptInvalid); !iter.IsDone(); iter++)
+            for (Child &child : Get<ChildTable>().Iterate(Child::kInStateAnyExceptInvalid))
             {
-                IgnoreError(mIndirectSender.RemoveMessageFromSleepyChild(*message, *iter.GetChild()));
+                IgnoreError(mIndirectSender.RemoveMessageFromSleepyChild(*message, child));
             }
         }
 

src/core/thread/mle_router.cpp

@@ -330,11 +330,11 @@ void MleRouter::SetStateRouter(uint16_t aRloc16)
     Get<Mac::Mac>().SetBeaconEnabled(true);
 
     // remove children that do not have matching RLOC16
-    for (ChildTable::Iterator iter(GetInstance(), Child::kInStateValidOrRestoring); !iter.IsDone(); iter++)
+    for (Child &child : Get<ChildTable>().Iterate(Child::kInStateValidOrRestoring))
     {
-        if (RouterIdFromRloc16(iter.GetChild()->GetRloc16()) != mRouterId)
+        if (RouterIdFromRloc16(child.GetRloc16()) != mRouterId)
         {
-            RemoveNeighbor(*iter.GetChild());
+            RemoveNeighbor(child);
         }
     }
 }
@@ -370,11 +370,11 @@ void MleRouter::SetStateLeader(uint16_t aRloc16)
     Get<AddressResolver>().Clear();
 
     // remove children that do not have matching RLOC16
-    for (ChildTable::Iterator iter(GetInstance(), Child::kInStateValidOrRestoring); !iter.IsDone(); iter++)
+    for (Child &child : Get<ChildTable>().Iterate(Child::kInStateValidOrRestoring))
     {
-        if (RouterIdFromRloc16(iter.GetChild()->GetRloc16()) != mRouterId)
+        if (RouterIdFromRloc16(child.GetRloc16()) != mRouterId)
         {
-            RemoveNeighbor(*iter.GetChild());
+            RemoveNeighbor(child);
         }
     }
 
@@ -1835,9 +1835,8 @@ void MleRouter::HandleStateUpdateTimer(void)
     }
 
     // update children state
-    for (ChildTable::Iterator iter(GetInstance(), Child::kInStateAnyExceptInvalid); !iter.IsDone(); iter++)
+    for (Child &child : Get<ChildTable>().Iterate(Child::kInStateAnyExceptInvalid))
     {
-        Child &  child   = *iter.GetChild();
         uint32_t timeout = 0;
 
         switch (child.GetState())
@@ -2124,14 +2123,14 @@ otError MleRouter::UpdateChildAddresses(const Message &aMessage, uint16_t aOffse
         // table is timed out and then trying to register its globally unique
         // IPv6 address as the new child.
 
-        for (ChildTable::Iterator iter(GetInstance(), Child::kInStateValidOrRestoring); !iter.IsDone(); iter++)
+        for (Child &child : Get<ChildTable>().Iterate(Child::kInStateValidOrRestoring))
         {
-            if (iter.GetChild() == &aChild)
+            if (&child == &aChild)
             {
                 continue;
             }
 
-            IgnoreError(iter.GetChild()->RemoveIp6Address(address));
+            IgnoreError(child.RemoveIp6Address(address));
         }
 
         // Clear EID-to-RLOC cache for the unicast address registered by the child.
@@ -2728,9 +2727,8 @@ void MleRouter::SynchronizeChildNetworkData(void)
 {
     VerifyOrExit(IsRouterOrLeader(), OT_NOOP);
 
-    for (ChildTable::Iterator iter(GetInstance(), Child::kInStateValid); !iter.IsDone(); iter++)
+    for (Child &child : Get<ChildTable>().Iterate(Child::kInStateValid))
     {
-        Child & child = *iter.GetChild();
         uint8_t version;
 
         if (child.IsRxOnWhenIdle())
@@ -3452,7 +3450,6 @@ Neighbor *MleRouter::GetNeighbor(const Mac::Address &aAddress)
 Neighbor *MleRouter::GetNeighbor(const Ip6::Address &aAddress)
 {
     Lowpan::Context context;
-    Child *         child;
     Neighbor *      rval = nullptr;
 
     if (aAddress.IsLinkLocal())
@@ -3468,19 +3465,17 @@ Neighbor *MleRouter::GetNeighbor(const Ip6::Address &aAddress)
         context.mContextId = 0xff;
     }
 
-    for (ChildTable::Iterator iter(GetInstance(), Child::kInStateValidOrRestoring); !iter.IsDone(); iter++)
+    for (Child &child : Get<ChildTable>().Iterate(Child::kInStateValidOrRestoring))
     {
-        child = iter.GetChild();
-
         if ((context.mContextId == kMeshLocalPrefixContextId) && aAddress.GetIid().IsLocator() &&
-            (aAddress.GetIid().GetLocator() == child->GetRloc16()))
+            (aAddress.GetIid().GetLocator() == child.GetRloc16()))
         {
-            ExitNow(rval = child);
+            ExitNow(rval = &child);
         }
 
-        if (child->HasIp6Address(aAddress))
+        if (child.HasIp6Address(aAddress))
         {
-            ExitNow(rval = child);
+            ExitNow(rval = &child);
         }
     }
 
@@ -3752,9 +3747,9 @@ void MleRouter::RefreshStoredChildren(void)
 {
     SuccessOrExit(Get<Settings>().DeleteChildInfo());
 
-    for (ChildTable::Iterator iter(GetInstance(), Child::kInStateAnyExceptInvalid); !iter.IsDone(); iter++)
+    for (Child &child : Get<ChildTable>().Iterate(Child::kInStateAnyExceptInvalid))
     {
-        SuccessOrExit(StoreChild(*iter.GetChild()));
+        SuccessOrExit(StoreChild(child));
     }
 
 exit:
@@ -4110,9 +4105,9 @@ void MleRouter::HandleAddressSolicitResponse(Coap::Message *         aMessage,
     IgnoreError(SendLinkRequest(nullptr));
 
     // send child id responses
-    for (ChildTable::Iterator iter(GetInstance(), Child::kInStateChildIdRequest); !iter.IsDone(); iter++)
+    for (Child &child : Get<ChildTable>().Iterate(Child::kInStateChildIdRequest))
     {
-        IgnoreError(SendChildIdResponse(*iter.GetChild()));
+        IgnoreError(SendChildIdResponse(child));
     }
 
 exit:
@@ -4671,9 +4666,9 @@ bool MleRouter::HasChildren(void)
 
 void MleRouter::RemoveChildren(void)
 {
-    for (ChildTable::Iterator iter(GetInstance(), Child::kInStateValidOrRestoring); !iter.IsDone(); iter++)
+    for (Child &child : Get<ChildTable>().Iterate(Child::kInStateValidOrRestoring))
     {
-        RemoveNeighbor(*iter.GetChild());
+        RemoveNeighbor(child);
     }
 }
 
@@ -4711,10 +4706,8 @@ otError MleRouter::GetMaxChildTimeout(uint32_t &aTimeout) const
 
     VerifyOrExit(IsRouterOrLeader(), error = OT_ERROR_INVALID_STATE);
 
-    for (ChildTable::Iterator iter(GetInstance(), Child::kInStateValid); !iter.IsDone(); iter++)
+    for (Child &child : Get<ChildTable>().Iterate(Child::kInStateValid))
     {
-        Child &child = *iter.GetChild();
-
         if (child.IsFullThreadDevice())
         {
             continue;
@@ -4783,10 +4776,8 @@ bool MleRouter::HasSleepyChildrenSubscribed(const Ip6::Address &aAddress)
 {
     bool rval = false;
 
-    for (ChildTable::Iterator iter(GetInstance(), Child::kInStateValidOrRestoring); !iter.IsDone(); iter++)
+    for (Child &child : Get<ChildTable>().Iterate(Child::kInStateValidOrRestoring))
     {
-        Child &child = *iter.GetChild();
-
         if (child.IsRxOnWhenIdle())
         {
             continue;

src/core/thread/network_diagnostic.cpp

@@ -241,12 +241,10 @@ otError NetworkDiagnostic::AppendChildTable(Message &aMessage)
 
     SuccessOrExit(error = aMessage.Append(&tlv, sizeof(ChildTableTlv)));
 
-    for (ChildTable::Iterator iter(GetInstance(), Child::kInStateValid); !iter.IsDone(); iter++)
+    for (Child &child : Get<ChildTable>().Iterate(Child::kInStateValid))
     {
         VerifyOrExit(count--, OT_NOOP);
 
-        Child &child = *iter.GetChild();
-
         timeout = 0;
 
         while (static_cast<uint32_t>(1 << timeout) < child.GetTimeout())

src/core/thread/src_match_controller.cpp

@@ -212,12 +212,12 @@ otError SourceMatchController::AddPendingEntries(void)
 {
     otError error = OT_ERROR_NONE;
 
-    for (ChildTable::Iterator iter(GetInstance(), Child::kInStateValidOrRestoring); !iter.IsDone(); iter++)
+    for (Child &child : Get<ChildTable>().Iterate(Child::kInStateValidOrRestoring))
     {
-        if (iter.GetChild()->IsIndirectSourceMatchPending())
+        if (child.IsIndirectSourceMatchPending())
         {
-            SuccessOrExit(error = AddAddress(*iter.GetChild()));
-            iter.GetChild()->SetIndirectSourceMatchPending(false);
+            SuccessOrExit(error = AddAddress(child));
+            child.SetIndirectSourceMatchPending(false);
         }
     }
 

src/core/utils/child_supervision.cpp

@@ -120,10 +120,8 @@ void ChildSupervisor::HandleTimer(void)
 {
     VerifyOrExit(mSupervisionInterval != 0, OT_NOOP);
 
-    for (ChildTable::Iterator iter(GetInstance(), Child::kInStateValid); !iter.IsDone(); iter++)
+    for (Child &child : Get<ChildTable>().Iterate(Child::kInStateValid))
     {
-        Child &child = *iter.GetChild();
-
         child.IncrementSecondsSinceLastSupervision();
 
         if ((child.GetSecondsSinceLastSupervision() >= mSupervisionInterval) && !child.IsRxOnWhenIdle())

tests/unit/test_child_table.cpp

@@ -144,97 +144,85 @@ void VerifyChildTableContent(ChildTable &aTable, uint16_t aChildListLength, cons
             VerifyOrQuit(ChildMatches(*child, aChildList[listIndex]), "FindChild(address) returned incorrect child");
         }
 
-        // Verify `ChildTable::Iterator` behavior when starting from different child entries.
+        // Verify `ChildTable::Iterator` behavior.
 
-        for (uint16_t listIndex = 0; listIndex <= aChildListLength; listIndex++)
         {
-            Child *startingChild = nullptr;
+            ChildTable::Iterator iter(*sInstance, filter);
+            bool                 childObserved[kMaxChildren];
+            uint16_t             numChildren = 0;
 
-            if (listIndex < aChildListLength)
+            memset(childObserved, 0, sizeof(childObserved));
+
+            // Use the iterator and verify that each returned `Child` entry is in the expected list.
+
+            for (; !iter.IsDone(); iter++)
             {
-                startingChild = aTable.FindChild(aChildList[listIndex].mRloc16, Child::kInStateAnyExceptInvalid);
-                VerifyOrQuit(startingChild != nullptr, "FindChild() failed");
-            }
+                Child *  child    = iter.GetChild();
+                Child &  childRef = *iter;
+                bool     didFind  = false;
+                uint16_t childIndex;
 
-            // Test an iterator starting from `startingChild`.
+                VerifyOrQuit(child != nullptr, "iter.GetChild() failed");
+                VerifyOrQuit(&childRef == child, "iter.operator*() failed");
+                VerifyOrQuit(iter->GetRloc16() == child->GetRloc16(), "iter.operator->() failed");
 
-            {
-                ChildTable::Iterator iter(*sInstance, filter, startingChild);
-                bool                 childObserved[kMaxChildren];
-                uint16_t             numChildren = 0;
-
-                memset(childObserved, 0, sizeof(childObserved));
-
-                // Check if the first entry matches the `startingChild`
-
-                if ((startingChild != nullptr) && StateMatchesFilter(startingChild->GetState(), filter))
-                {
-                    VerifyOrQuit(!iter.IsDone(), "iterator IsDone() failed");
-                    VerifyOrQuit(iter.GetChild() != nullptr, "iterator GetChild() failed");
-                    VerifyOrQuit(iter.GetChild() == startingChild,
-                                 "Iterator failed to start from the given child entry");
-
-                    iter++;
-                    iter.Reset();
-                    VerifyOrQuit(iter.GetChild() == startingChild, "iterator Reset() failed");
-                }
-
-                // Use the iterator and verify that each returned `Child` entry is in the expected list.
-
-                for (; !iter.IsDone(); iter++)
-                {
-                    Child *  child   = iter.GetChild();
-                    bool     didFind = false;
-                    uint16_t childIndex;
-
-                    VerifyOrQuit(child != nullptr, "iter.GetChild() failed");
-
-                    childIndex = aTable.GetChildIndex(*child);
-                    VerifyOrQuit(childIndex < aTable.GetMaxChildrenAllowed(), "Child Index is out of bound");
-                    VerifyOrQuit(aTable.GetChildAtIndex(childIndex) == child, "GetChildAtIndex() failed");
-
-                    for (uint16_t index = 0; index < aChildListLength; index++)
-                    {
-                        if (ChildMatches(*iter.GetChild(), aChildList[index]))
-                        {
-                            childObserved[index] = true;
-                            numChildren++;
-                            didFind = true;
-                            break;
-                        }
-                    }
-
-                    VerifyOrQuit(didFind, "ChildTable::Iterator returned an entry not in the expected list");
-                }
-
-                // Verify that when iterator is done, it points to `nullptr`.
-
-                VerifyOrQuit(iter.GetChild() == nullptr, "iterator GetChild() failed");
-
-                iter++;
-                VerifyOrQuit(iter.IsDone(), "iterator Advance() (after iterator is done) failed");
-                VerifyOrQuit(iter.GetChild() == nullptr, "iterator GetChild() failed");
-
-                // Verify that the number of children matches the number of entries we get from iterator.
-
-                VerifyOrQuit(aTable.GetNumChildren(filter) == numChildren, "GetNumChildren() failed");
-                VerifyOrQuit(aTable.HasChildren(filter) == (numChildren != 0), "HasChildren() failed");
-
-                // Verify that there is no missing or extra entry between the expected list
-                // and what was observed/returned by the iterator.
+                childIndex = aTable.GetChildIndex(*child);
+                VerifyOrQuit(childIndex < aTable.GetMaxChildrenAllowed(), "Child Index is out of bound");
+                VerifyOrQuit(aTable.GetChildAtIndex(childIndex) == child, "GetChildAtIndex() failed");
 
                 for (uint16_t index = 0; index < aChildListLength; index++)
                 {
-                    if (StateMatchesFilter(aChildList[index].mState, filter))
+                    if (ChildMatches(*iter.GetChild(), aChildList[index]))
                     {
-                        VerifyOrQuit(childObserved[index], "iterator failed to return an expected entry");
-                    }
-                    else
-                    {
-                        VerifyOrQuit(!childObserved[index], "iterator returned an extra unexpected entry");
+                        childObserved[index] = true;
+                        numChildren++;
+                        didFind = true;
+                        break;
                     }
                 }
+
+                VerifyOrQuit(didFind, "ChildTable::Iterator returned an entry not in the expected list");
             }
+
+            // Verify that when iterator is done, it points to `nullptr`.
+
+            VerifyOrQuit(iter.GetChild() == nullptr, "iterator GetChild() failed");
+
+            iter++;
+            VerifyOrQuit(iter.IsDone(), "iterator Advance() (after iterator is done) failed");
+            VerifyOrQuit(iter.GetChild() == nullptr, "iterator GetChild() failed");
+
+            // Verify that the number of children matches the number of entries we get from iterator.
+
+            VerifyOrQuit(aTable.GetNumChildren(filter) == numChildren, "GetNumChildren() failed");
+            VerifyOrQuit(aTable.HasChildren(filter) == (numChildren != 0), "HasChildren() failed");
+
+            // Verify that there is no missing or extra entry between the expected list
+            // and what was observed/returned by the iterator.
+
+            for (uint16_t index = 0; index < aChildListLength; index++)
+            {
+                if (StateMatchesFilter(aChildList[index].mState, filter))
+                {
+                    VerifyOrQuit(childObserved[index], "iterator failed to return an expected entry");
+                }
+                else
+                {
+                    VerifyOrQuit(!childObserved[index], "iterator returned an extra unexpected entry");
+                }
+            }
+
+            // Verify the behavior of range-based `for` iteration.
+
+            iter.Reset();
+
+            for (Child &child : aTable.Iterate(filter))
+            {
+                VerifyOrQuit(&child == iter.GetChild(), "range-based for loop Iterate() failed");
+                iter++;
+            }
+
+            VerifyOrQuit(iter.IsDone(), "range-based for loop Iterate() did not return all entries");
         }
     }