[locator] adding Get<Type> to InstanceLocator (#3714)

This commit changes how the objects in OpenThread access each other.
It adds a template `Get<Type>()` method in `InstanceLocator`. This
method returns a reference to a given `Type` object belonging to the
OpenThread instance (e.g. `Get<MeshForwarder>()` returns a reference
to `MeshForwarder` object on the OpenThread instance). The
`InstanceLocator` is used as base class of all OpenThread classes so
every class can easily access any other object. This commit also
changes how the main instance is retrieved in `InstanceLocator` for
the single-instance case. The method `GetInstance()` directly uses the
raw buffer `gInstanceRaw`. This change helps make the `GetInstance()`
and in turn all `Get<Type>()` methods in-line. This commit also
removes the existing getters across all classes to use the new
`Get<Type>()` model.

tests/unit/test_child.cpp

@@ -88,7 +88,7 @@ void VerifyChildIp6Addresses(const Child &aChild, uint8_t aAddressListLength, co
     {
         VerifyOrQuit(addressObserved[index], "Child::GetNextIp6Address() missed an entry from the expected list\n");
 
-        if (sInstance->GetThreadNetif().GetMle().IsMeshLocalAddress(aAddressList[index]))
+        if (sInstance->Get<Mle::MleRouter>().IsMeshLocalAddress(aAddressList[index]))
         {
             SuccessOrQuit(aChild.GetMeshLocalIp6Address(*sInstance, address),
                           "Child::GetMeshLocalIp6Address() failed\n");
@@ -127,7 +127,7 @@ void TestChildIp6Address(void)
     numAddresses = 0;
 
     // First addresses uses the mesh local prefix (mesh-local address).
-    addresses[numAddresses] = sInstance->GetThreadNetif().GetMle().GetMeshLocal64();
+    addresses[numAddresses] = sInstance->Get<Mle::MleRouter>().GetMeshLocal64();
     addresses[numAddresses].SetIid(meshLocalIid);
 
     numAddresses++;

tests/unit/test_lowpan.cpp

@@ -38,7 +38,6 @@ namespace ot {
 
 ot::Instance *  sInstance;
 Ip6::Ip6 *      sIp6;
-ThreadNetif *   sThreadNetif;
 Lowpan::Lowpan *sLowpan;
 
 void TestIphcVector::GetCompressedStream(uint8_t *aIphc, uint16_t &aIphcLength)
@@ -110,7 +109,7 @@ void TestIphcVector::GetUncompressedStream(Message &aMessage)
 static void Init()
 {
     otMeshLocalPrefix meshLocalPrefix = {{0xfd, 0x00, 0xca, 0xfe, 0xfa, 0xce, 0x12, 0x34}};
-    sThreadNetif->GetMle().SetMeshLocalPrefix(meshLocalPrefix);
+    sInstance->Get<Mle::MleRouter>().SetMeshLocalPrefix(meshLocalPrefix);
 
     // Emulate global prefixes with contextes.
     uint8_t mockNetworkData[] = {
@@ -128,12 +127,12 @@ static void Init()
         0x02, 0x40                                                              // Context ID = 2, C = FALSE
     };
 
-    Message *message = sInstance->GetMessagePool().New(Message::kTypeIp6, 0);
+    Message *message = sInstance->Get<MessagePool>().New(Message::kTypeIp6, 0);
     VerifyOrQuit(message != NULL, "6lo: Ip6::NewMessage failed");
 
     SuccessOrQuit(message->Append(mockNetworkData, sizeof(mockNetworkData)), "6lo: Message::Append failed");
 
-    sThreadNetif->GetNetworkDataLeader().SetNetworkData(0, 0, true, *message, 0);
+    sInstance->Get<NetworkData::Leader>().SetNetworkData(0, 0, true, *message, 0);
 }
 
 /**
@@ -180,7 +179,7 @@ static void Test(TestIphcVector &aVector, bool aCompress, bool aDecompress)
     {
         Lowpan::BufferWriter buffer(result, 127);
 
-        VerifyOrQuit((message = sInstance->GetMessagePool().New(Message::kTypeIp6, 0)) != NULL,
+        VerifyOrQuit((message = sInstance->Get<MessagePool>().New(Message::kTypeIp6, 0)) != NULL,
                      "6lo: Ip6::NewMessage failed");
 
         aVector.GetUncompressedStream(*message);
@@ -210,7 +209,7 @@ static void Test(TestIphcVector &aVector, bool aCompress, bool aDecompress)
 
     if (aDecompress)
     {
-        VerifyOrQuit((message = sInstance->GetMessagePool().New(Message::kTypeIp6, 0)) != NULL,
+        VerifyOrQuit((message = sInstance->Get<MessagePool>().New(Message::kTypeIp6, 0)) != NULL,
                      "6lo: Ip6::NewMessage failed");
 
         int decompressedBytes =
@@ -1754,9 +1753,8 @@ void TestLowpanIphc(void)
 
     VerifyOrQuit(sInstance != NULL, "NULL instance");
 
-    sIp6         = &sInstance->GetIp6();
-    sThreadNetif = &sInstance->GetThreadNetif();
-    sLowpan      = &sThreadNetif->GetLowpan();
+    sIp6    = &sInstance->Get<Ip6::Ip6>();
+    sLowpan = &sInstance->Get<Lowpan::Lowpan>();
 
     Init();
 

tests/unit/test_message.cpp

@@ -45,7 +45,7 @@ void TestMessage(void)
     instance = static_cast<ot::Instance *>(testInitInstance());
     VerifyOrQuit(instance != NULL, "Null OpenThread instance\n");
 
-    messagePool = &instance->GetMessagePool();
+    messagePool = &instance->Get<ot::MessagePool>();
 
     for (unsigned i = 0; i < sizeof(writeBuffer); i++)
     {

tests/unit/test_message_queue.cpp

@@ -86,7 +86,7 @@ void TestMessageQueue(void)
     sInstance = testInitInstance();
     VerifyOrQuit(sInstance != NULL, "Null instance");
 
-    sMessagePool = &sInstance->GetMessagePool();
+    sMessagePool = &sInstance->Get<ot::MessagePool>();
 
     for (int i = 0; i < kNumTestMessages; i++)
     {

tests/unit/test_ncp_buffer.cpp

@@ -381,7 +381,7 @@ void TestNcpFrameBuffer(void)
     NcpFrameBuffer::WritePosition pos1, pos2;
 
     sInstance    = testInitInstance();
-    sMessagePool = &sInstance->GetMessagePool();
+    sMessagePool = &sInstance->Get<MessagePool>();
 
     for (i = 0; i < sizeof(buffer); i++)
     {
@@ -1006,7 +1006,7 @@ void TestFuzzNcpFrameBuffer(void)
     uint32_t lensArrayCount[kNumPrios];
 
     sInstance    = testInitInstance();
-    sMessagePool = &sInstance->GetMessagePool();
+    sMessagePool = &sInstance->Get<MessagePool>();
 
     memset(buffer, 0, sizeof(buffer));
 

tests/unit/test_priority_queue.cpp

@@ -220,7 +220,7 @@ void TestPriorityQueue(void)
     instance = testInitInstance();
     VerifyOrQuit(instance != NULL, "Null OpenThread instance\n");
 
-    messagePool = &instance->GetMessagePool();
+    messagePool = &instance->Get<ot::MessagePool>();
 
     // Use the function "New()" to allocate messages with different priorities
     for (int i = 0; i < kNumNewPriorityTestMessages; i++)