Immutable struct cannot be read back

[dm3]

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Are immutable structs supposed to work with FlatBuffers? I couldn't make the serialization/deserialization work both with and without the @STRUCT annotation.

I've added the following code under the TestInt8I struct definition in test/runtests.jl to get a smallest reproducible case:

struct TestInt8I
    x::Int8
end

inst2 = TestInt8I(2)
b = FlatBuffers.Builder(TestInt8I)
FlatBuffers.build!(b, inst2)
t = FlatBuffers.Table(b)
inst2_1 = FlatBuffers.read(t)

@test inst2.x == inst2_1.x

The the test fails with:

ERROR: LoadError: EOFError: read end of file
Stacktrace:
 [1] unsafe_read(::Base.AbstractIOBuffer{SubArray{UInt8,1,Array{UInt8,1},Tuple{UnitRange{Int64}},true}}, ::Ptr{UInt8}, ::UInt64) at ./iobuffer.jl:105
 [2] unsafe_read(::Base.AbstractIOBuffer{SubArray{UInt8,1,Array{UInt8,1},Tuple{UnitRange{Int64}},true}}, ::Base.RefValue{Int32}, ::Int64) at ./io.jl:361
 [3] read at ./io.jl:363 [inlined]
 [4] read at ./io.jl:367 [inlined]
 [5] get(::FlatBuffers.Table{TestInt8I}, ::Int64, ::Type{Int32}) at /Users/dm3/.julia/v0.6/FlatBuffers/src/internals.jl:8
 [6] offset(::FlatBuffers.Table{TestInt8I}, ::Int64) at /Users/dm3/.julia/v0.6/FlatBuffers/src/internals.jl:18
 [7] read(::FlatBuffers.Table{TestInt8I}, ::Type{TestInt8I}) at /Users/dm3/.julia/v0.6/FlatBuffers/src/FlatBuffers.jl:218
 [8] read(::FlatBuffers.Table{TestInt8I}) at /Users/dm3/.julia/v0.6/FlatBuffers/src/FlatBuffers.jl:210
 [9] include_from_node1(::String) at ./loading.jl:576
 [10] include(::String) at ./sysimg.jl:14
 [11] process_options(::Base.JLOptions) at ./client.jl:305
 [12] _start() at ./client.jl:371
while loading /Users/dm3/.julia/v0.6/FlatBuffers/test/runtests.jl, in expression starting on line 64

[rjkat]

Immutable structs are supposed to work, but they can’t be the “root type”. See https://github.com/google/flatbuffers/issues/4657