# TOML: using to\_toml option may produce incorrect TOML

**URL:** <https://discourse.julialang.org/t/toml-using-to-toml-option-may-produce-incorrect-toml/86157>\
**Category:** General Usage\
**Tags:** toml\
**Created:** [August 22, 2022, 9:22pm UTC](https://discourse.julialang.org/t/toml-using-to-toml-option-may-produce-incorrect-toml/86157 "2022-08-22T21:22:32Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![stephenll](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stephenll/32/28751_2.png) [@stephenll](https://discourse.julialang.org/u/stephenll)\
**Post date:** [August 22, 2022, 9:22pm UTC](https://discourse.julialang.org/t/toml-using-to-toml-option-may-produce-incorrect-toml/86157/1 "2022-08-22T21:22:32Z")

</div>

This is a simplified example to illustrate the issue I’m seeing with using the TOML writer with the `to_toml` option for writing a custom type. It seems that when using the to\_toml option, TOML print doesn’t print the correct TOML.

I expect the `hello = "hello"` to not be combined with the `[b]` table.

I’m using Julia 1.8 Silicon on an M1 Mac.

Just looking to see if anyone else is seeing this and if my understanding is correct.

```julia
using TOML

struct Foo
    a::Int64
    b::Float64
end

struct Bar
    c::Float64
    d::String
end

f = Foo(2,9.9)
b = Bar(1.345, "hello")

dd = Dict("hello"=>"world", "f"=>f, "b"=>b)

toDict(foo::Foo) = Dict("a"=>foo.a, "b"=>foo.b)
toDict(bar::Bar) = Dict("c"=>bar.c, "d"=>bar.d)

TOML.print(toDict,dd)

```

which results in the “hello” being added to the `b` table in the TOML.

```julia
[f]
b = 9.9
a = 2

[b]
c = 1.345
d = "hello"
hello = "world"

```

---

<div class="post-metadata">

**Author:** ![digital\_carver](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/digital_carver/32/33818_2.png) [@digital\_carver](https://discourse.julialang.org/u/digital_carver)\
**Post date:** [August 23, 2022, 3:52am UTC](https://discourse.julialang.org/t/toml-using-to-toml-option-may-produce-incorrect-toml/86157/2 "2022-08-23T03:52:01Z")

</div>

This does seem to be a bug in TOML.jl. It happens when there’s a simple (non-Dict) entry like `"hello" => "world"` along with custom entries like `f` and `b` here that become `Dict`s only after the conversion function.

(Internally, it tries to print all the simple non-Dict entries first, but when something turns out to be not a simple value after conversion, it immediately prints it with a recursive call

```julia
        if is_tabular(value)
            _print(f, io, Dict(key => value); indent, first_block, sorted, by)

```

rather than defer it for later after all the non-Dict entries have been printed.)