Erlang Standard Context

This is the Erlang Standard Context Package. Context is an opaque carrier of data. It it not meant to replace Erlang's standard ways of working with data such as lists, dict, maps. etc.

Getting Started

When developing applications using Erlang it's sometimes desirable to thread some sort of opaque Context object to ease in working with but not limited to caching, tracing and various data to keep local state.

Programs that use Contexts should follow these rules to keep interfaces consistent across packages:

Do not store Contexts; instead, pass a Context explicitly to each function that needs it. The Context should be the first parameter, typically named ctx:

init() ->
  Ctx = context:new(),
  context:set(Ctx, start_ts, os:timestamp()).

handle_request(Ctx, Arg) ->
  Req = context:get(Ctx, req),
  %% ...
  {ok, Ctx}

terminate(Ctx) ->
  Duration = timer:now_diff(os:timestamp(), context:get(Ctx, start_ts)),
  ok.

Use context Values only for request-scoped data that transits processes and APIs, not for passing optional parameters to functions.

If you update data on the context be sure to return the updated context. A good pattern for returning context and/or data from functions is:

%% Update context and return an updated context.
update_ctx(Ctx0) ->
  Ctx1 = context:set(Ctx0, key, value),
  {ok, Ctx1}.

%% Update context and return an updated context and data.
return_data(Ctx0) ->
  Ctx1 = context:set(Ctx0, key, value),
  Data = <<"...">>,
  {ok, {Ctx1, Data}}.

Dependencies

None

Versioning

We use SemVer for versioning. For the versions available, see the tags on this repository.

Authors

• Kivra - Initial work - Kivra

License

This project is licensed under the MIT License - see the LICENSE file for details