C++: mini_reflect: Add DefaultTypeTable

[emaxerrno]

Currently it's very easy to make a mistake when it comes to
instantiating the TypeTable to print a buffer because it is not type
safe.

This will allow us to write safer cpp code:

flatbuffers::FlatBufferToString(reinterpret_cast<const uint8_t *>(&t),
decltype(t)::DefaultTypeTable());

[emaxerrno]

@gwvo

I had a file that was like this:

ostream &
operator<<(ostream &o, const ::smf::wal::tx_put_fragment &f) {
  o << "tx_put_fragment="
    << flatbuffers::FlatBufferToString(reinterpret_cast<const uint8_t *>(&f),
                                       tx_put_fragmentTypeTable());
  return o;
}


ostream &
operator<<(ostream &o, const tx_get_request &r) {
  o << "tx_get_request="
    << flatbuffers::FlatBufferToString(reinterpret_cast<const uint8_t *>(&r),
                                       tx_get_requestTypeTable());
  return o;
}
ostream &
operator<<(ostream &o, const tx_get_reply &r) {
  o << "tx_get_reply="
    << flatbuffers::FlatBufferToString(reinterpret_cast<const uint8_t *>(&r),
                                       tx_get_replyTypeTable());
  return o;
}

...
...

I had a few core_dumps and then realize it was a typo on the name.

I can write a type safe quick wrapper with this change.

[emaxerrno]

All the unit tests are passing now

test 1
Start 1: flattests

1: Test command: /home/agallego/workspace/flatbuffers/build/flattests
1: Test timeout computed to be: 9.99988e+06
1: ALL TESTS PASSED
1/1 Test #1: flattests ........................ Passed 0.06 sec

100% tests passed, 0 tests failed out of 1

Total Test time (real) = 0.06 sec

[emaxerrno]

one can then create a simple helper like this

template< typename T>
struct fbs_print{
   fbs_print(const uint8_t *x):data(x){}

   inline flatbuffers::TypeTable* print() { return T::DefaultTypeTable(); }
   const uint8_t * data;
};

std::ostream operator<<(std::ostream &o, const fbs_print<Foo> &any{
   return o << any.print();
}

....

then you can it it on your code as 

char* buf = ... 

std::cout << fbs_print<MonsterType>(buf) << std::endl;

[aardappel]

Please make sure the * goes next to the name. Also, Default doesn't sound quite right, since there are no alternatives. Just TypeTable would be too prone to clashes. Maybe.. ThisTypeTable ? GetTypeTable ? TheTypeTable ? Or go verbose and say MiniReflectTypeTable..?

[emaxerrno]

Sounds good, will submit fix. Thanks!

[emaxerrno]

Sounds good, I fixed it, let me know if you want me to do any other edits.

[aardappel]

Thanks!