Error deserializing multiple values of custom struct

[GregPlowman]

Is this expected to work?

using Serialization

function writedata(filename::AbstractString, itr)
    open(filename, "w") do io
        s = Serializer(io)
        Serialization.writeheader(s)
        for x in itr
            serialize(s, x)
        end
    end
end

function readdata(filename::AbstractString)
    open(filename, "r") do io
        while !eof(io)
            @show deserialize(io)
        end
    end
end

This code using native Int produces the expected output:

filename = "test.jls"
writedata(filename, [i for i = 1:3])
readdata(filename)

deserialize(io) = 1
deserialize(io) = 2
deserialize(io) = 3

But attempting this with a custom struct, errors on the second deserialize.

struct Foo
    a::Int
end
writedata(filename, [Foo(i) for i = 1:3])
readdata(filename)

deserialize(io) = Foo(1)
ERROR: KeyError: key 0 not found
Stacktrace:
 [1] getindex at .\abstractdict.jl:599 [inlined]
 [2] handle_deserialize(::Serializer{IOStream}, ::Int32) at C:\cygwin\home\Administrator\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.1\Serialization\src\Serialization.jl:764
 [3] deserialize(::Serializer{IOStream}) at C:\cygwin\home\Administrator\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.1\Serialization\src\Serialization.jl:731
 [4] handle_deserialize(::Serializer{IOStream}, ::Int32) at C:\cygwin\home\Administrator\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.1\Serialization\src\Serialization.jl:778
 [5] deserialize(::IOStream) at C:\cygwin\home\Administrator\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.1\Serialization\src\Serialization.jl:731
 [6] macro expansion at .\show.jl:555 [inlined]
 [7] (::getfield(Main, Symbol("##7#8")))(::IOStream) at .\REPL[3]:4
 [8] #open#310(::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{(),Tuple{}}}, ::Function, ::getfield(Main, Symbol("##7#8")), ::String, ::Vararg{String,N} where N) at .\iostream.jl:369
 [9] open at .\iostream.jl:367 [inlined]
 [10] readdata(::String) at .\REPL[3]:2
 [11] top-level scope at none:0

[JeffBezanson]

The values were written with the same Serializer context, so there can be shared references within the stream. They need to be deserialized using the same context object as well.

[GregPlowman]

Right. Thank you.

So readdata should be something like:

function readdata(filename::AbstractString)
   open(filename, "r") do io
        s = Serializer(io)
        while !eof(io)
            @show deserialize(s)
        end
    end
end

[StefanKarpinski]

Perhaps the error message could be improved?