[erlang-questions] 12B4 dialyzer problem 6 - strings
Mon Sep 22 14:04:11 CEST 2008
Anthony Shipman wrote:
> I've got some code that accesses a driver and it looks like this:
> 119: -spec parseDate(string()) -> integer() | badarg.
> parseDate(Date) when is_list(Date) ->
> Port = open(),
> N = parseDate(Port, Date),
> ok = close(Port),
> -spec parseDate(port(), string()) -> integer() | badarg.
> parseDate(Port, Date) when is_port(Port), is_list(Date) ->
> Bin = port_control(Port, ?CMD_PDATE, Date),
> Dialyzer says, with -Wunderspecs,
> dwcAuxDrv.erl:119: Type specification dwcAuxDrv:parseDate/1 :: (string())
> -> integer() | 'badarg' is a supertype of the success typing: ([byte()])
> -> 'badarg' | integer()
> I thought that string() and [byte()] would be the same. But delving into the
> source code I find that a string() is a [char()] and a char() is an integer
> in the range 0..16#10ffff (from hipe erl_types.erl). So there's a
> contradiction in there.
I'm not sure that it is contradicting, but yes it might be a bit
surprising. Richard Carlsson set this limit when he implemented the
original type domain, and I have just left it as is. Basically it is a
trade-off to allow people to call their lists of integers strings even
if they do not follow the [byte()] limit.
In general, the warnings that you get when using -Wunderspecs (and
friends) is something you might want to look at, but not necessarily fix.
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