Added a way to get mutable tables out of a mutable vector of tables.

Change-Id: I8f9ef1d14f86671ced929c7a159115b1d8510327
Tested: on Linux.

include/flatbuffers/flatbuffers.h

@@ -207,6 +207,7 @@ template<typename T> size_t AlignOf() {
 // (avoiding the need for a trailing return decltype)
 template<typename T> struct IndirectHelper {
   typedef T return_type;
+  typedef T mutable_return_type;
   static const size_t element_stride = sizeof(T);
   static return_type Read(const uint8_t *p, uoffset_t i) {
     return EndianScalar((reinterpret_cast<const T *>(p))[i]);
@@ -214,6 +215,7 @@ template<typename T> struct IndirectHelper {
 };
 template<typename T> struct IndirectHelper<Offset<T>> {
   typedef const T *return_type;
+  typedef T *mutable_return_type;
   static const size_t element_stride = sizeof(uoffset_t);
   static return_type Read(const uint8_t *p, uoffset_t i) {
     p += i * sizeof(uoffset_t);
@@ -222,6 +224,7 @@ template<typename T> struct IndirectHelper<Offset<T>> {
 };
 template<typename T> struct IndirectHelper<const T *> {
   typedef const T *return_type;
+  typedef T *mutable_return_type;
   static const size_t element_stride = sizeof(T);
   static return_type Read(const uint8_t *p, uoffset_t i) {
     return reinterpret_cast<const T *>(p + i * sizeof(T));
@@ -306,6 +309,7 @@ public:
   uoffset_t Length() const { return size(); }
 
   typedef typename IndirectHelper<T>::return_type return_type;
+  typedef typename IndirectHelper<T>::mutable_return_type mutable_return_type;
 
   return_type Get(uoffset_t i) const {
     assert(i < size());
@@ -347,6 +351,12 @@ public:
     WriteScalar(data() + i, val - (Data() + i * sizeof(uoffset_t)));
   }
 
+  // Get a mutable pointer to tables/strings inside this vector.
+  mutable_return_type GetMutableObject(uoffset_t i) const {
+    assert(i < size());
+    return const_cast<mutable_return_type>(IndirectHelper<T>::Read(Data(), i));
+  }
+
   // The raw data in little endian format. Use with care.
   const uint8_t *Data() const {
     return reinterpret_cast<const uint8_t *>(&length_ + 1);

tests/test.cpp

@@ -108,6 +108,7 @@ flatbuffers::unique_ptr_t CreateFlatBufferTest(std::string &buffer) {
   mlocs[0] = mb1.Finish();
   MonsterBuilder mb2(builder);
   mb2.add_name(barney);
+  mb2.add_hp(1000);
   mlocs[1] = mb2.Finish();
   MonsterBuilder mb3(builder);
   mb3.add_name(wilma);
@@ -203,6 +204,7 @@ void AccessFlatBufferTest(const uint8_t *flatbuf, size_t length) {
   for (auto it = vecoftables->begin(); it != vecoftables->end(); ++it)
     TEST_EQ(strlen(it->name()->c_str()) >= 4, true);
   TEST_EQ_STR(vecoftables->Get(0)->name()->c_str(), "Barney");
+  TEST_EQ(vecoftables->Get(0)->hp(), 1000);
   TEST_EQ_STR(vecoftables->Get(1)->name()->c_str(), "Fred");
   TEST_EQ_STR(vecoftables->Get(2)->name()->c_str(), "Wilma");
   TEST_NOTNULL(vecoftables->LookupByKey("Barney"));
@@ -260,6 +262,13 @@ void MutateFlatBuffersTest(uint8_t *flatbuf, std::size_t length) {
   TEST_EQ(inventory->Get(9), 100);
   inventory->Mutate(9, 9);
 
+  auto tables = monster->mutable_testarrayoftables();
+  auto first = tables->GetMutableObject(0);
+  TEST_EQ(first->hp(), 1000);
+  first->mutate_hp(0);
+  TEST_EQ(first->hp(), 0);
+  first->mutate_hp(1000);
+
   // Run the verifier and the regular test to make sure we didn't trample on
   // anything.
   AccessFlatBufferTest(flatbuf, length);