Why the need for a Root

[lbensaad]

What is the reason of using a root type. If i have Request and Response tables to be sent between two parties, so why we could not create them separately. A buffer could contain either a Request or a Response. In fact any message(Table) should be able to a root in a buffer.

[ghost]

Any table can be a root in a buffer. The root type is mostly for use by JSON, which doesn't specify any types, so we need to know where to start. The generated GetRoot functions are merely convenience.

[lbensaad]

Ok, thanks. But in Java,

1. If i have a ByteBuffer of a non root table how do read that using FlatBuffersBuilder. The only way I know is to use the __init() function, is there another way?
2. Is there a way to know the type of the table from the binary data?
3. How to use the addXXXType function, in your JavaTest.java you used: Monster.addTestType(fbb, (byte)1); how do you get the type of a table, in this case 1 which it is hard-coded ?

[ghost]

1. a commit was pushed yesterday that adds GetRootAs functions for all tables, not just the root_type.

2. generally no. this is a strongly types system, meaning you need to know the kind of buffer you're dealing with. If you want to use this in a context where you want to have multiple different root types, you have these options:
   a) make your root type a table that contains a union of all possible sub-roots.
   b) prefix flatbuffers with your own file header
   c) use flatbuffer's built-in file indentification feature, which hasn't been ported to Java yet. I'll get to that.

3. That's a bug, the 1 should actually read: Any.Monster. I'll fix that.

[lbensaad]

Thanks

1. But i think the name should be just "get" or "init" instead of getRootAs

[ghost]

getRootAs is a bit more descriptive and less likely to clash with other identifiers. I think I'll keep it for now.

To further my response to your issue #2, the built-in file_identifier functionality is now also available in Java. See the Schema docs, Java docs, and Java code.

[let4be]

So... How do I access non root_type buffers, can't find anything like Get*** in c++ generated files and the same problem in go lang.
generated code has huge differencies between languages and it's really hard to work with

[let4be]

Tried both latest master and latest release versions

[ghost]

In C++ there is the GetRoot templated function that works with any table type.
Go appears to still be pending on: #363

[gaurimaheshwari]

please explain me how to build flatc executable?

[aardappel]

@gaurimaheshwari : https://google.github.io/flatbuffers/flatbuffers_guide_building.html