:erlang.term_to_binary/1 returns unexpected/incorrect binary for integer lists

Hey @KalleJoP I also get the same result, but Erlang at least seems to have no problem converting it back to a list:

iex(1)> [2] |> :erlang.term_to_binary |> :erlang.binary_to_term
[2]

Can you elaborate why you expect <<131, 108, 0, 0, 0, 1, 97, 2, 106>>?

out of curiosity I just

iex(1)> :erlang.binary_to_term <<131, 108, 0, 0, 0, 1, 97, 2, 106>>                                                
[2]
iex(2)> :erlang.binary_to_term <<131, 107, 0, 1, 2>>                                                               
[2]
iex(3) (:erlang.binary_to_term <<131, 108, 0, 0, 0, 1, 97, 2, 106>>) == (:erlang.binary_to_term <<131, 107, 0, 1, 2>>)
true

That’s the missing parenthesis . Without the parenthesis round your function calls that I think line is being interpreted as

: erlang.binary_to_term(<<131, 108, 0, 0, 0, 1, 97, 2, 106>>  == :erlang.binary_to_term<<131, 107, 0, 1, 2>>)   

which is the same as

erlang.binary_to_term(false)

iex(1)> :erlang.binary_to_term(<<131, 108, 0, 0, 0, 1, 97, 2, 106>>) == :erlang.binary_to_term(<<131, 107, 0, 1, 2>>)  
true

I don’t know off the top of my head why the the two binary forms are equivalent. I could guess but I am trying to avoid being further nerd sniped by this question right now. :-/

Seems like there’s a list and string type:

Sounds like there’s overlap for charlists.

yes, I just found I was missing the parenthesis! Puzzled and intrigued too…

There are no parenthesis missing

I edited my previous post without making it evident my bad

Thank you.. I don’t know why I’m always so scared to go an look into Erlang docs ..

I found out that the problem is the decoding on java side. I use the OtpErlang package and for some reason, they decode small integer lists to strings.

You can view it here:
https://github.com/erlang/otp/blob/517443b5207970f84642ba29629410bfd0ff69f5/lib/jinterface/java_src/com/ericsson/otp/erlang/OtpExternal.java#L66

https://github.com/erlang/otp/blob/f9cdb96f3ab07b378a66ebfb1473184374f4e16f/lib/jinterface/java_src/com/ericsson/otp/erlang/OtpInputStream.java#L1257

Heh

iex(1)> :erlang.term_to_binary('hello') 
<<131, 107, 0, 5, 104, 101, 108, 108, 111>>
iex(2)> :erlang.term_to_binary('🧐')   
<<131, 108, 0, 0, 0, 1, 98, 0, 1, 249, 208, 106>>
iex(3)> '🧐'
[129488]
iex(4)> :erlang.term_to_binary([129488])
<<131, 108, 0, 0, 0, 1, 98, 0, 1, 249, 208, 106>>

[Edit] - For a minute I’d fooled myself into thinking that Erlang was intentionally supporting unicode in charlists but I wasn’t thinking straight. It’s just an artefact of Elixir’s charlist support

iex(1)> cs = 'hello 🧐'
[104, 101, 108, 108, 111, 32, 129488]
iex(2)> :erlang.iolist_to_binary(cs)
** (ArgumentError) errors were found at the given arguments:

  * 1st argument: not an iodata term

    :erlang.iolist_to_binary([104, 101, 108, 108, 111, 32, 129488])
    iex:2: (file)

``

Also 

> Only if a string contains code points < 256, can it be directly converted to a binary 

https://www.erlang.org/doc/apps/stdlib/unicode_usage.html#standard-unicode-representation