Erlang: supervisor:start_child/2 error has me baffled - erlang

Question

I'm making slight modifications to Logan/Merritt/Carlson's simple cache, Chapter 6, pp 149-169, Erlang and OTP in Action. So far, no code changes, just renaming the modules.
I start the application:
application:start(gridz).
ok
I insert an item:
gridz_maker:insert(blip, blop).
I get this error:
** exception error: no match of right hand side value
{error,
{function_clause,
[{gridz_edit,init,
[{blop,86400}],
[{file,"src/gridz_edit.erl"},{line,51}]},
{gen_server,init_it,6,
[{file,"gen_server.erl"},{line,304}]},
{proc_lib,init_p_do_apply,3,
[{file,"proc_lib.erl"},{line,227}]}]}}
in function gridz_maker:insert/2 (src/gridz_maker.erl, line 15)
Here's the code:
insert(Key, Value) ->
case gridz_store:lookup(Key) of
{ok, Pid} -> gridz_edit:replace(Pid, Value);
{error, _} -> {ok, Pid} = gridz_edit:create(Value), %% line 15
gridz_store:insert(Key, Pid)
end.
I look at line 15:
{error, _} -> {ok, Pid} = gridz_edit:create(Value),
I expect the error because this is a new item. gridz:edit is a gen_server (sc_element in Logan et/al.) Here's the code for create/1:
create(Value) ->
create(Value, ?DEFAULT_LEASE_TIME).
create(Value, LeaseTime) ->
gridz_sup:start_child(Value, LeaseTime).
And here's the code for gridz_sup:start_child/2:
start_child(Value, LeaseTime) ->
supervisor:start_child(?SERVER, [Value, LeaseTime]).
init([]) ->
Grid = {gridz_edit, {gridz_edit, start_link, []},
temporary, brutal_kill, worker, [gridz_edit]},
Children = [Grid],
RestartStrategy = {simple_one_for_one, 0, 1},
{ok, {RestartStrategy, Children}}.
If I execute supervisor:start_child/2 directly, here's what I get:
{error,{function_clause,[{gridz_edit,init,
[{blop,50400}],
[{file,"src/gridz_edit.erl"},{line,51}]},
{gen_server,init_it,6,
[{file,"gen_server.erl"},{line,304}]},
{proc_lib,init_p_do_apply,3,
[{file,"proc_lib.erl"},{line,227}]}]}}
Line 51 in gridz_edit is an init function:
init([Value, LeaseTime]) ->
Now = calendar:local_time(),
StartTime = calendar:datetime_to_gregorian_seconds(Now),
{ok,
#state{value = Value,
lease_time = LeaseTime,
start_time = StartTime},
time_left(StartTime, LeaseTime)}.
If I execute it directly, it works:
120> gridz_edit:init([blop, (60 * 60 * 24)]).
{ok,{state,blop,86400,63537666408},86400000}
So now I'm baffled. What am I missing? Why does supervisor:start_child/2 throw an error?
Thanks,
LRP

Answer 1

The error says you are passing in a tuple with 2 members, {blop,86400}, when you seem to be expecting a list of 2 members: [Value, LeaseTime]. In your direct execution, you are also using a list, so it works. You should figure out where the tuple is being created, and create a list instead.