Many warnings when compiling with elixir 1.3

[jeanparpaillon]

elixir 1.3 deprecates some languages features used in ewebmachine, producing a lot of warnings

[jeanparpaillon]

Most of ewebmachine macros use the (anti-hygienic) var! construction in macros for producing side-effects (ie affect context's conn and user_state variables).

• PRO: side effect provided through syntaxic sugar, no runtime override
• CON: if used inside a if/cond/... construction, implies unsafe use of variables, which is deprecated

Alternatives are:

1. no side-effect: all functions takes explicitly conn and user_state variables and returns a
   copy of them:

   • PRO: no side effect
   • CON: heavier syntax, big API change

2. no side effect, with simplified callbacks: all callbacks have a simplified version macro, without
   conn and user_state variable available

   • PRO: no side effect, clean syntax
   • CON: (limited) API change: when using simplified macros, conn and state are not available anymore

   is_conflict(conn, state) -> {boolean(), conn, state}
   is_conflict -> boolean()

3. side effect through process dictionary: original webmachine implementation

   • PRO: light syntax
   • CON: performance

4. side effect through external process:

   • each request processing process (P1) is attached another process (Agent ?, ets table ?, P2) storing conn and user_state
   • P1 process dictionary stores only P2 pid
   • PRO: no API change, clean syntax
   • CON: performance between 1-2 and 3 ?

[jeanparpaillon]

Fixed in 7dc4157