# Naive use of BSON not working as expected

**URL:** <https://discourse.julialang.org/t/naive-use-of-bson-not-working-as-expected/25740>\
**Category:** Data\
**Created:** [June 26, 2019, 6:33pm UTC](https://discourse.julialang.org/t/naive-use-of-bson-not-working-as-expected/25740 "2019-06-26T18:33:45Z")\
**Posts on this page:** 16\
**Page:** 1

<div class="post-metadata">

**Author:** ![ablaom](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ablaom/32/4889_2.png) [@ablaom](https://discourse.julialang.org/u/ablaom)\
**Post date:** [June 26, 2019, 6:33pm UTC](https://discourse.julialang.org/t/naive-use-of-bson-not-working-as-expected/25740/1 "2019-06-26T18:33:45Z")

</div>

Sorry, I am a beginner to BSON and am a little stuck.

I have a struct `Foo` defined entirely in some package A. Package B imports A, defines an instance `f=A.Foo()` and serializes that instance using BSON.

Now if, in the REPL, I do `import A; using BSON` and attempt to  
restore `f` then there is no problem. But if put _identical code_ into  
a new package C (having B as a dependency) then I get `UndefVarError: A not defined`. Why is that?

---

<div class="post-metadata">

**Author:** ![PetrKryslUCSD](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/petrkryslucsd/32/215825_2.png) [@PetrKryslUCSD](https://discourse.julialang.org/u/PetrKryslUCSD)\
**Post date:** [June 26, 2019, 6:53pm UTC](https://discourse.julialang.org/t/naive-use-of-bson-not-working-as-expected/25740/2 "2019-06-26T18:53:48Z")

</div>

MWE available?

---

<div class="post-metadata">

**Author:** ![ablaom](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ablaom/32/4889_2.png) [@ablaom](https://discourse.julialang.org/u/ablaom)\
**Post date:** [June 27, 2019, 8:30am UTC](https://discourse.julialang.org/t/naive-use-of-bson-not-working-as-expected/25740/3 "2019-06-27T08:30:00Z")

</div>

**package A**

Here is the contents of A/src/A.jl:

```julia
module A

struct Foo
    x::Int
end

end # module

```

**package C**

Here is the contents of C/src/C.jl

```julia
module C

import A
using BSON

file = "/Users/anthony/test.bson"
f = BSON.load(file)[:f]
@show f

end # module

```

**serializing and deserialising in the REPL**

```julia
julia> import A
       using BSON

       f = A.Foo(7)

       file = "/Users/anthony/test.bson"
       bson(file, Dict(:f=>f))        

humus:toml anthony$ julia # restarting the REPL

julia> import A
       using BSON
       file = "/Users/anthony/test.bson"
       f = BSON.load(file)[:f]
A.Foo(7) # working as expected

```

**instead importing C to deserialise:**

```julia
julia> using C
[Info: Precompiling C [371b88f8-98b2-11e9-0613-bf108cd8ab40]
ERROR: LoadError: UndefVarError: A not defined
Stacktrace:
 [1] (::getfield(BSON, Symbol("##31#32")))(::Module, ::String) at /Users/anthony/.julia/packages/BSON/XPZLD/src/extensions.jl:20
 [2] mapfoldl_impl(::typeof(identity), ::getfield(BSON, Symbol("##31#32")), ::NamedTuple{(:init,),Tuple{Module}}, ::Array{Any,1}) at ./reduce.jl:45
 [3] #mapfoldl#187(::Base.Iterators.Pairs{Symbol,Module,Tuple{Symbol},NamedTuple{(:init,),Tuple{Module}}}, ::Function, ::Function, ::Function, ::Array{Any,1}) at ./reduce.jl:72
 [4] #mapfoldl at ./none:0 [inlined]
 [5] _mapreduce_dim at ./reducedim.jl:306 [inlined]
 [6] #mapreduce#548 at ./reducedim.jl:304 [inlined]
 [7] #mapreduce at ./none:0 [inlined]
 [8] #reduce#549 at ./reducedim.jl:348 [inlined]
 [9] (::getfield(Base, Symbol("#kw##reduce")))(::NamedTuple{(:init,),Tuple{Module}}, ::typeof(reduce), ::Function, ::Array{Any,1}) at ./none:0
 [10] resolve(::Array{Any,1}) at /Users/anthony/.julia/packages/BSON/XPZLD/src/extensions.jl:20
 [11] (::getfield(BSON, Symbol("##35#36")))(::Dict{Symbol,Any}) at /Users/anthony/.julia/packages/BSON/XPZLD/src/extensions.jl:48
 [12] _raise_recursive(::Dict{Symbol,Any}, ::IdDict{Any,Any}) at /Users/anthony/.julia/packages/BSON/XPZLD/src/read.jl:79
 [13] raise_recursive(::Dict{Symbol,Any}, ::IdDict{Any,Any}) at /Users/anthony/.julia/packages/BSON/XPZLD/src/read.jl:89
 [14] (::getfield(BSON, Symbol("##45#46")))(::Dict{Symbol,Any}, ::IdDict{Any,Any}) at /Users/anthony/.julia/packages/BSON/XPZLD/src/extensions.jl:133
 [15] raise_recursive(::Dict{Symbol,Any}, ::IdDict{Any,Any}) at /Users/anthony/.julia/packages/BSON/XPZLD/src/read.jl:88
 [16] (::getfield(BSON, Symbol("##20#22")){IdDict{Any,Any}})(::Dict{Symbol,Any}) at /Users/anthony/.julia/packages/BSON/XPZLD/src/read.jl:82
 [17] applychildren!(::getfield(BSON, Symbol("##20#22")){IdDict{Any,Any}}, ::Dict{Symbol,Any}) at /Users/anthony/.julia/packages/BSON/XPZLD/src/BSON.jl:21
 [18] _raise_recursive(::Dict{Symbol,Any}, ::IdDict{Any,Any}) at /Users/anthony/.julia/packages/BSON/XPZLD/src/read.jl:82
 [19] raise_recursive(::Dict{Symbol,Any}, ::IdDict{Any,Any}) at /Users/anthony/.julia/packages/BSON/XPZLD/src/read.jl:89
 [20] raise_recursive at /Users/anthony/.julia/packages/BSON/XPZLD/src/read.jl:99 [inlined]
 [21] load(::String) at /Users/anthony/.julia/packages/BSON/XPZLD/src/read.jl:104
 [22] top-level scope at none:0
 [23] include at ./boot.jl:326 [inlined]
 [24] include_relative(::Module, ::String) at ./loading.jl:1038
 [25] include(::Module, ::String) at ./sysimg.jl:29
 [26] top-level scope at none:2
 [27] eval at ./boot.jl:328 [inlined]
 [28] eval(::Expr) at ./client.jl:404
 [29] top-level scope at ./none:3
in expression starting at /Users/anthony/Dropbox/Julia7/MLJ/MLJ/sandbox/toml/C/src/C.jl:7
ERROR: Failed to precompile C [371b88f8-98b2-11e9-0613-bf108cd8ab40] to /Users/anthony/.julia/compiled/v1.1/C/6eWus.ji.
Stacktrace:
 [1] error(::String) at ./error.jl:33
 [2] compilecache(::Base.PkgId, ::String) at ./loading.jl:1197
 [3] _require(::Base.PkgId) at ./loading.jl:960
 [4] require(::Base.PkgId) at ./loading.jl:858
 [5] require(::Module, ::Symbol) at ./loading.jl:853

```

---

<div class="post-metadata">

**Author:** ![PetrKryslUCSD](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/petrkryslucsd/32/215825_2.png) [@PetrKryslUCSD](https://discourse.julialang.org/u/PetrKryslUCSD)\
**Post date:** [June 27, 2019, 9:42am UTC](https://discourse.julialang.org/t/naive-use-of-bson-not-working-as-expected/25740/4 "2019-06-27T09:42:01Z")

</div>

This works for me:

```julia
julia>
Julia has exited. Press Enter to start a new session.

Starting Julia...
[Info: Recompiling stale cache file C:\Users\PK\.julia\compiled\v1.3\Atom\w9XOh.ji for Atom [c52e3926-4ff0-5f6e-af25-54175e0327b1]
               _
   _ _ _(_)_ | Documentation: https://docs.julialang.org
  (_) | (_) (_) |
   _ _ _| |_ __ _ | Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` | |
  | | |_| | | | (_| | | Version 1.3.0-DEV.359 (2019-06-04)
 _/ |\ __'_|_|_|\__'_| | Commit b54bc8d7e8 (22 days old master)
|__/ |

julia> include("A.jl")
Main.A

julia> import Main.A

julia> 

julia> using BSON

julia> 

julia> f = A.Foo(7)
Main.A.Foo(7)

julia> 

julia> file = "./test.bson"
"./test.bson"

julia> 

julia> bson(file, Dict(:f=>f))

julia> include("C.jl")
f = Main.A.Foo(7)
Main.C

julia> 

```

No changes other than referring to `Main.A`.

---

<div class="post-metadata">

**Author:** ![ablaom](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ablaom/32/4889_2.png) [@ablaom](https://discourse.julialang.org/u/ablaom)\
**Post date:** [June 27, 2019, 12:24pm UTC](https://discourse.julialang.org/t/naive-use-of-bson-not-working-as-expected/25740/5 "2019-06-27T12:24:51Z")

</div>

Yes, thank you for looking at this!

Unfortunately, this doesn’t resolve my issue. Yes, I can _include_ C.jl, but it I import the C _package_ I get the error (for reasons I don’t understand). Since I need deserialization from within a package, my problem remains.

---

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**Author:** ![PetrKryslUCSD](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/petrkryslucsd/32/215825_2.png) [@PetrKryslUCSD](https://discourse.julialang.org/u/PetrKryslUCSD)\
**Post date:** [June 27, 2019, 3:06pm UTC](https://discourse.julialang.org/t/naive-use-of-bson-not-working-as-expected/25740/6 "2019-06-27T15:06:29Z")

</div>

So what exactly do you do to be able to do `import A`? You have a package project file?  
How does one reproduce your problem?

---

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**Author:** ![ablaom](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ablaom/32/4889_2.png) [@ablaom](https://discourse.julialang.org/u/ablaom)\
**Post date:** [June 27, 2019, 3:15pm UTC](https://discourse.julialang.org/t/naive-use-of-bson-not-working-as-expected/25740/7 "2019-06-27T15:15:44Z")

</div>

Project file for package A (no dependencies):

```julia
name = "A"
uuid = "224fedf6-98b2-11e9-382a-43c3b7668a47"
version = "0.1.0"

```

Project file for package C:

```julia
name = "C"
uuid = "371b88f8-98b2-11e9-0613-bf108cd8ab40"
version = "0.1.0"

[deps]
A = "224fedf6-98b2-11e9-382a-43c3b7668a47"
BSON = "fbb218c0-5317-5bc6-957e-2ee96dd4b1f0"

```

---

<div class="post-metadata">

**Author:** ![PetrKryslUCSD](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/petrkryslucsd/32/215825_2.png) [@PetrKryslUCSD](https://discourse.julialang.org/u/PetrKryslUCSD)\
**Post date:** [June 27, 2019, 3:42pm UTC](https://discourse.julialang.org/t/naive-use-of-bson-not-working-as-expected/25740/8 "2019-06-27T15:42:45Z")

</div>

So you did `]add A` and `]add C`?  
And then `import A `?  
EDIT: On second thought, perhaps rather `dev`?

---

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**Author:** ![PetrKryslUCSD](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/petrkryslucsd/32/215825_2.png) [@PetrKryslUCSD](https://discourse.julialang.org/u/PetrKryslUCSD)\
**Post date:** [June 27, 2019, 3:54pm UTC](https://discourse.julialang.org/t/naive-use-of-bson-not-working-as-expected/25740/9 "2019-06-27T15:54:54Z")

</div>

> [@ablaom](#):
>
> using C

Okay, I think I understand the problem. When you do `using C` the module `A` is not known.  
It needs to be added to the dependencies of `C`.

---

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**Author:** ![ablaom](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ablaom/32/4889_2.png) [@ablaom](https://discourse.julialang.org/u/ablaom)\
**Post date:** [June 27, 2019, 5:05pm UTC](https://discourse.julialang.org/t/naive-use-of-bson-not-working-as-expected/25740/10 "2019-06-27T17:05:12Z")

</div>

A is a dependency of C. See project file above.

And yes, generate the packages with Pkg.generate(“A”) and Pkg.generate(“C”), populate the source files with the code above, activate the project for `C` and `dev` BSON and A to make them dependencies of `C`.

---

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**Author:** ![PetrKryslUCSD](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/petrkryslucsd/32/215825_2.png) [@PetrKryslUCSD](https://discourse.julialang.org/u/PetrKryslUCSD)\
**Post date:** [June 27, 2019, 5:40pm UTC](https://discourse.julialang.org/t/naive-use-of-bson-not-working-as-expected/25740/11 "2019-06-27T17:40:49Z")

</div>

Yes, but how do you set up the computation when you start Julia? If you start Julia and immediately do `using C`, I think `A` will not be loaded at that point.

---

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**Author:** ![ablaom](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ablaom/32/4889_2.png) [@ablaom](https://discourse.julialang.org/u/ablaom)\
**Post date:** [June 27, 2019, 7:48pm UTC](https://discourse.julialang.org/t/naive-use-of-bson-not-working-as-expected/25740/12 "2019-06-27T19:48:00Z")

</div>

This also does not work:

```julia
julia> using A
julia> using C
[Info: Precompiling C [371b88f8-98b2-11e9-0613-bf108cd8ab40]
ERROR: LoadError: UndefVarError: A not defined
Stacktrace:
 [1] (::getfield(BSON, Symbol("##31#32")))(::Module, ::String) at /Users/anthony/.julia/packages/BSON/XPZLD/src/extensions.jl:20
 [2] mapfoldl_impl(::typeof(identity), ::getfield(BSON, Symbol("##31#32")), ::NamedTuple{(:init,),Tuple{Module}}, ::Array{Any,1}) at ./reduce.jl:45
 [3] #mapfoldl#187(::Base.Iterators.Pairs{Symbol,Module,Tuple{Symbol},NamedTuple{(:init,),Tuple{Module}}}, ::Function, ::Function, ::Function, ::Array{Any,1}) at ./reduce.jl:72
 [4] #mapfoldl at ./none:0 [inlined]
 [5] _mapreduce_dim at ./reducedim.jl:306 [inlined]
 [6] #mapreduce#548 at ./reducedim.jl:304 [inlined]
 [7] #mapreduce at ./none:0 [inlined]
 [8] #reduce#549 at ./reducedim.jl:348 [inlined]
 [9] (::getfield(Base, Symbol("#kw##reduce")))(::NamedTuple{(:init,),Tuple{Module}}, ::typeof(reduce), ::Function, ::Array{Any,1}) at ./none:0
 [10] resolve(::Array{Any,1}) at /Users/anthony/.julia/packages/BSON/XPZLD/src/extensions.jl:20
 [11] (::getfield(BSON, Symbol("##35#36")))(::Dict{Symbol,Any}) at /Users/anthony/.julia/packages/BSON/XPZLD/src/extensions.jl:48
 [12] _raise_recursive(::Dict{Symbol,Any}, ::IdDict{Any,Any}) at /Users/anthony/.julia/packages/BSON/XPZLD/src/read.jl:79
 [13] raise_recursive(::Dict{Symbol,Any}, ::IdDict{Any,Any}) at /Users/anthony/.julia/packages/BSON/XPZLD/src/read.jl:89
 [14] (::getfield(BSON, Symbol("##45#46")))(::Dict{Symbol,Any}, ::IdDict{Any,Any}) at /Users/anthony/.julia/packages/BSON/XPZLD/src/extensions.jl:133
 [15] raise_recursive(::Dict{Symbol,Any}, ::IdDict{Any,Any}) at /Users/anthony/.julia/packages/BSON/XPZLD/src/read.jl:88
 [16] (::getfield(BSON, Symbol("##20#22")){IdDict{Any,Any}})(::Dict{Symbol,Any}) at /Users/anthony/.julia/packages/BSON/XPZLD/src/read.jl:82
 [17] applychildren!(::getfield(BSON, Symbol("##20#22")){IdDict{Any,Any}}, ::Dict{Symbol,Any}) at /Users/anthony/.julia/packages/BSON/XPZLD/src/BSON.jl:21
 [18] _raise_recursive(::Dict{Symbol,Any}, ::IdDict{Any,Any}) at /Users/anthony/.julia/packages/BSON/XPZLD/src/read.jl:82
 [19] raise_recursive(::Dict{Symbol,Any}, ::IdDict{Any,Any}) at /Users/anthony/.julia/packages/BSON/XPZLD/src/read.jl:89
 [20] raise_recursive at /Users/anthony/.julia/packages/BSON/XPZLD/src/read.jl:99 [inlined]
 [21] load(::String) at /Users/anthony/.julia/packages/BSON/XPZLD/src/read.jl:104
 [22] top-level scope at none:0
 [23] include at ./boot.jl:326 [inlined]
 [24] include_relative(::Module, ::String) at ./loading.jl:1038
 [25] include(::Module, ::String) at ./sysimg.jl:29
 [26] top-level scope at none:2
 [27] eval at ./boot.jl:328 [inlined]
 [28] eval(::Expr) at ./client.jl:404
 [29] top-level scope at ./none:3
in expression starting at /Users/anthony/Dropbox/Julia7/MLJ/MLJ/sandbox/toml/C/src/C.jl:7
ERROR: Failed to precompile C [371b88f8-98b2-11e9-0613-bf108cd8ab40] to /Users/anthony/.julia/compiled/v1.1/C/6eWus.ji.
Stacktrace:
 [1] error(::String) at ./error.jl:33
 [2] compilecache(::Base.PkgId, ::String) at ./loading.jl:1197
 [3] _require(::Base.PkgId) at ./loading.jl:960
 [4] require(::Base.PkgId) at ./loading.jl:858
 [5] require(::Module, ::Symbol) at ./loading.jl:853

```

---

<div class="post-metadata">

**Author:** ![ablaom](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ablaom/32/4889_2.png) [@ablaom](https://discourse.julialang.org/u/ablaom)\
**Post date:** [June 29, 2019, 6:56am UTC](https://discourse.julialang.org/t/naive-use-of-bson-not-working-as-expected/25740/13 "2019-06-29T06:56:28Z")

</div>

As @ayush-1506 has pointed out to me, the explanation for the behaviour is in BSON/src/extenstions.jl, line 20:

```julia
resolve(fs) = reduce((m, f) -> getfield(m, Symbol(f)), fs; init = Main

```

I think this means that the expressions parsed by the deserialiser are always resolved in the Main namespace, rather than in the namespace of the module calling `BSON.load`.

This seems like an unnecessary restriction.

---

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**Author:** ![jpsamaroo](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jpsamaroo/32/46804_2.png) [@jpsamaroo](https://discourse.julialang.org/u/jpsamaroo)\
**Post date:** [June 29, 2019, 6:38pm UTC](https://discourse.julialang.org/t/naive-use-of-bson-not-working-as-expected/25740/14 "2019-06-29T18:38:57Z")

</div>

I believe the reason for this is that the only other easy option is loading within the module that `BSON.load` executes in, which is always going to be BSON (because that’s where it’s defined). Not saying it can’t resolve elsewhere; someone would just need to thread the appropriate argument down the call stack.

---

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**Author:** ![PetrKryslUCSD](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/petrkryslucsd/32/215825_2.png) [@PetrKryslUCSD](https://discourse.julialang.org/u/PetrKryslUCSD)\
**Post date:** [June 29, 2019, 6:40pm UTC](https://discourse.julialang.org/t/naive-use-of-bson-not-working-as-expected/25740/15 "2019-06-29T18:40:19Z")

</div>

I think you are right. It bombs there, in BSON. The Main restriction is weird, but at least that would be readily circumvented in your code.

---

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**Author:** ![JonasIsensee](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jonasisensee/32/4704_2.png) [@JonasIsensee](https://discourse.julialang.org/u/JonasIsensee)\
**Post date:** [June 29, 2019, 7:09pm UTC](https://discourse.julialang.org/t/naive-use-of-bson-not-working-as-expected/25740/16 "2019-06-29T19:09:35Z")

</div>

I believe you may have encountered the same problem as described in

[https://github.com/MikeInnes/BSON.jl/issues/25](https://github.com/MikeInnes/BSON.jl/issues/25)