I have the following function:
-spec check_connection_header(list()) -> atom().
check_connection_header([{<<"Connection">>, <<"close">>}|_]) ->
close;
check_connection_header([{<<"Connection">>, <<"Close">>}|_]) ->
close;
check_connection_header([{<<"connection">>, <<"close">>}|_]) ->
close;
check_connection_header([{<<"connection">>, <<"Close">>}|_]) ->
close;
check_connection_header([_|Rest]) ->
check_connection_header(Rest);
check_connection_header([])->
keep_alive.
And when i run dialyzer I get the following output:
131: The pattern [{<<67:8/integer-unit:1,111:8/integer-unit:1,110:8/integer-unit:1,110:8/integer-unit:1,101:8/integer-unit:1,99:8/integer-unit:1,116:8/integer-unit:1,105:8/integer-unit:1,111:8/integer-unit:1,110:8/integer-unit:1>>, <<99:8/integer-unit:1,108:8/integer-unit:1,111:8/integer-unit:1,115:8/integer-unit:1,101:8/integer-unit:1>>} | _] can never match the type []
134: The pattern [{<<67:8/integer-unit:1,111:8/integer-unit:1,110:8/integer-unit:1,110:8/integer-unit:1,101:8/integer-unit:1,99:8/integer-unit:1,116:8/integer-unit:1,105:8/integer-unit:1,111:8/integer-unit:1,110:8/integer-unit:1>>, <<67:8/integer-unit:1,108:8/integer-unit:1,111:8/integer-unit:1,115:8/integer-unit:1,101:8/integer-unit:1>>} | _] can never match the type []
137: The pattern [{<<99:8/integer-unit:1,111:8/integer-unit:1,110:8/integer-unit:1,110:8/integer-unit:1,101:8/integer-unit:1,99:8/integer-unit:1,116:8/integer-unit:1,105:8/integer-unit:1,111:8/integer-unit:1,110:8/integer-unit:1>>, <<99:8/integer-unit:1,108:8/integer-unit:1,111:8/integer-unit:1,115:8/integer-unit:1,101:8/integer-unit:1>>} | _] can never match the type []
140: The pattern [{<<99:8/integer-unit:1,111:8/integer-unit:1,110:8/integer-unit:1,110:8/integer-unit:1,101:8/integer-unit:1,99:8/integer-unit:1,116:8/integer-unit:1,105:8/integer-unit:1,111:8/integer-unit:1,110:8/integer-unit:1>>, <<67:8/integer-unit:1,108:8/integer-unit:1,111:8/integer-unit:1,115:8/integer-unit:1,101:8/integer-unit:1>>} | _] can never match the type []
143: The pattern [_ | Rest] can never match the type []
I am pretty new to dialyzer and have trouble interpreting the output of dialyzer. I understand it is saying that the first 5 clauses of the function can't match [], but that is deliberate from my part since I'm matching the empty list in the sixth clause.
My erlang version is Erlang/OTP 19.0 and my dialyzer version is v3.0.
A interesting discover was that dialyzer does'nt complain about the above code when i run dialyzer v2.8 and Erlang/OTP 18 on another machine.
Things I've tried so far:
I'm not very experienced with binaries in erlang so my initial thought was that I had misunderstood the binary pattern matching, but this seems not to be the case. The function passes my test cases (calling the function with [] as parameter is no problem), and also if I replace the binaries with normal strings in the function heads I get the same complaints by dialyzer.
Rebuilt the plt and cleaned the project
Thanks in advance
The reason for the dialyzer warnings was that the function was always called with empty list ([]) due to a defect in my code.
So to conclude: Dialyzer was not wrong this time either :)