Printing references as strings?

This worked for me:

iex(5)> "#{inspect make_ref}"        
"#Reference<0.4290490855.1120927745.192473>"

Never used references before but it seems it can be printed just fine. Or are you looking for a certain property?

Don’t expect to. A reference is just a marker to a “place and time”. They’re usually otherwise empty values that are “guaranteed” to be unique. Now, sometimes they are coopted by the vm to refer to “something” but by and large they aren’t references like references in the JVM.

For example, let me send a call to another process. When the response comes back, it should somehow refer to the initial call, so that this response isn’t structurally confused for a callback for some other call (that maybe got dropped and thus orphaned). The thing that the call sends, which should be packaged with the response, so that it can be can referred back to correctly is a reference.

demo, you can see the return address PID and a reference packaged with the call content quite clearly:

iex(1)> self()
#PID<0.105.0>
iex(2)> pid = spawn(fn -> receive do any -> any end |> IO.inspect end) # trap the next message and print it
#PID<0.108.0>
iex(3)> GenServer.call(pid, :foo) # pretend the spawned thread is a genserver so we can peek inside the message

{:"$gen_call", {#PID<0.105.0>, #Reference<0.27482903.3541827588.143960>}, :foo}

(followed by the call failing because the called pid has stopped itself)

make_ref()
|> :erlang.ref_to_list()
|> List.to_string()

** (UndefinedFunctionError) function :erlang.reference_to_string/1 is undefined or private. Did you mean one of:

      * ref_to_list/1

    :erlang.reference_to_string(#Reference<0.1918863630.4161011720.226556>)

Yeah, sorry, it should be :erlang.ref_to_list/1.

I should clarify the use here: I’m working on a (mostly academic) exercise that seeks to run code in multiple modules, sometimes with different runtime values given to the same module, so I want a unique identifier for each “instance” (if you’ll forgive the OO speak). A reference seemed the most appropriate way to do this. The script may generate a lot of output which will be useful for reporting and data analysis, so a CSV or similar representation makes a lot of practical sense. So the question is simply how to represent the unique reference as a string inside of a CSV or similar file. inspect/1 is fine inside iex, but for the purposes of analysis, a simple textual representation is the only thing that wouldn’t look “weird”.

Plan B would be to use a UUID.

Remember that references are meant to be unique only within single cluster, there is no guarantee for global uniqueness of the reference, in contrast to UUID.

Uuids also have a slightly weak guarantee. Collisions are possible. However, you’ll probably be ok.

Much stronger than make_ref/0 (64 bits vs 122 bits, which with birthday collision will provide 10¹⁰ difference factor in possible collisions). And generating UUID can be done also outside of the BEAM, which is clearly a win for me.