Why are keys of a Dict not unpacked before serialization?

[simsurace]

Is this intentional? Values of a dict are unpacked before serialization, but keys are not:

using JSON3, StructTypes

struct IntWrapper
    val::Int
end

StructTypes.StructType(::Type{IntWrapper}) = StructTypes.NumberType()
StructTypes.numbertype(::Type{IntWrapper}) = Int
Base.Int(id::IntWrapper) = id.val

JSON3.write(IntWrapper(42)) == "42" # true
JSON3.write(Dict(IntWrapper(42) => 42)) == "{\"42\":42}" # false
JSON3.write(Dict(42 => IntWrapper(42))) == "{\"42\":42}" # true

Am I missing something or is this a bug?

[Naunet]

JSON only allows string keys.

It would appear that the dictionary keys are indeed being unwrapped since the result is a string and not a structure. However they then get "stringified" to be acceptable keys.

Some related discussions that may help you find a work-around:

• Reading and writing is broken for Dicts with struct keys · Issue #71 · quinnj/JSON3.jl · GitHub 1
• https://discourse.julialang.org/t/json3-read-dict-tuple-int-int-t-unexpected-behavior/117759

[quinnj]

Yeah, we have to ensure we produce valid JSON when writing

[simsurace]

Thanks, this makes sense!