FlatBuffers
|
There's experimental support for reading FlatBuffers in Go. Generate code for Go with the -g
option to flatc
.
See go_test.go
for an example. You import the generated code, read a FlatBuffer binary file into a []byte
, which you pass to the GetRootAsMonster
function:
Now you can access values like this:
Note that whenever you access a new object like in the Pos
example above, a new temporary accessor object gets created. If your code is very performance sensitive (you iterate through a lot of objects), you can replace nil with a pointer to a Vec3
object you've already created. This allows you to reuse it across many calls and reduce the amount of object allocation (and thus garbage collection) your program does.
To access vectors you pass an extra index to the vector field accessor. Then a second method with the same name suffixed by Length
let's you know the number of elements you can access:
You can also construct these buffers in Go using the functions found in the generated code, and the FlatBufferBuilder class:
Create strings:
Create a table with a struct contained therein:
Unlike C++, Go does not support table creation functions like 'createMonster()'. This is to create the buffer without using temporary object allocation (since the Vec3
is an inline component of Monster
, it has to be created right where it is added, whereas the name and the inventory are not inline, and must be created outside of the table creation sequence). Structs do have convenient methods that allow you to construct them in one call. These also have arguments for nested structs, e.g. if a struct has a field a
and a nested struct field b
(which has fields c
and d
), then the arguments will be a
, c
and d
.
Vectors also use this start/end pattern to allow vectors of both scalar types and structs:
The generated method 'StartInventoryVector' is provided as a convenience function which calls 'StartVector' with the correct element size of the vector type which in this case is 'ubyte' or 1 byte per vector element. You pass the number of elements you want to write. You write the elements backwards since the buffer is being constructed back to front. Use the correct Prepend
call for the type, or PrependUOffsetT
for offsets. You then pass inv
to the corresponding Add
call when you construct the table containing it afterwards.
There are Prepend
functions for all the scalar types. You use PrependUOffset
for any previously constructed objects (such as other tables, strings, vectors). For structs, you use the appropriate create
function in-line, as shown above in the Monster
example.
Once you're done constructing a buffer, you call Finish
with the root object offset (mon
in the example above). Your data now resides in Builder.Bytes. Important to note is that the real data starts at the index indicated by Head(), for Offset() bytes (this is because the buffer is constructed backwards). If you wanted to read the buffer right after creating it (using GetRootAsMonster
above), the second argument, instead of 0
would thus also be Head()
.
There currently is no support for parsing text (Schema's and JSON) directly from Go, though you could use the C++ parser through cgo. Please see the C++ documentation for more on text parsing.