CODEWITHSUNDEEP
stringerlang
Tommy
Tommy

Reputation: 13672

Erlang: DRYing up string+binary concatenation

I am currently forming strings from strings and binaries like this:

X = string:join(io_lib:format("~s~s~s", ["something1", "something2",<<"something3">>]), "") %X is now something1something2something3

This seems painful and messy. Because in order to dry this up with another such string with a different number of "~n":

Y = string:join(io_lib:format("~s~s", ["something1", <<"something2">>]), "")

I essentially have to write a function that counts the size of the argument list, and forms ~n[that many times] and plugs it into this.

Is there a better way to be doing this?

Eshell V8.0.2 (abort with ^G) 1> F = <<"asdf">>, 1> string:join(io_lib:format("~s~s~s", ["something1", "something2", F]),""). "something1something2asdf" 2> lists:flatten(["something1", "something2", F]). [115,111,109,101,116,104,105,110,103,49,115,111,109,101,116, 104,105,110,103,50,<<"asdf">>] 3>

Upvotes: 1

Views: 389

Answers (1)

Justin Niessner
Justin Niessner

Reputation: 245519

I'm confused as to why you need the call to io_lib:format at all. It's not doing any work in this case.

string:join(["something1","something2","something3"], "").

Would give you the same result. You can simplify even further if there's really no separator character (and taking advantage of the fact that strings are just lists in Erlang):

lists:flatten(["something1", "something2", "something3"]).

Update

I see now that you're working with a list of different data types. While a one-liner may look pretty, you can see that they're not always flexible. In your case, I would create some mapper functions to handle mapping different types to strings. Maybe something like:

-module(string_utils).
-export([concat/1]).

to_string(Value) when is_binary(Value) -> binary_to_list(Value);
to_string(Value) -> Value.
concat(List) ->
  lists:flatten(lists:map(fun to_string/1, List)).

And then your calling code would be:

string_utils:concat(["something1", "something2", <<"something3">>]).

Upvotes: 4

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