Elixir 1.2 is out, and this is the second minor release since Elixir in Action has been published, so I wanted to discuss some consequences of new releases on the book’s material.

Since the book focuses on concurrency and OTP principles, most of its content is still up to date. OTP is at this point pretty stable and not likely to be significantly changed. Moreover, Elixir 1.2 is mostly downwards compatible, meaning that the code written for earlier 1.x versions should compile and work on 1.2. In some cases, some minor modifications might be required, in which case the compiler should emit a corresponding error/warning.

All that said, some information in the book is not completely accurate anymore, so I’d like to point out a few things.

Updated code examples

Some minor changes had to be made to make the code examples work, most notably relaxing the versioning requirement in mix.exs. You can find the 1.2 compliant code examples here.

Deprecating Dict and Set

Elixir 1.2 requires Erlang 18.x which brings a couple of big changes. You can see the highlights here, but in the context of EiA, the most important improvement deals with maps which now perform well for large datasets. Consequently, HashDict and HashSet are becoming redundant.

Therefore the Elixir core team decided to deprecate following k-v and set related modules: Dict, Set, HashDict, and HashSet. These modules are soft deprecated, meaning that they will in fact still work, but their usage is discouraged as they are marked for subsequent removal. If you’re developing for Elixir 1.2+ you’re encouraged to use plain maps for k-v structure, and the new type MapSet (internally also powered by maps) for sets.

There’s one important caveat: if your code must work on Elixir 1.0 and 1.1, then you should in fact still prefer HashDict and HashSet. The reason is that the older Elixir version can run on Erlang 17, so if your code uses large maps, the performance might suffer.

For Elixir in Action, this means that all the code that’s using HashDict should be changed to use maps. Most notably, the Todo.List abstraction should internally use maps to maintain the entries field. You can see the changes in this commit.

Protocol consolidation

Starting Elixir 1.2, protocols are consolidated by default in all build environments (you can change this by setting consolidate_protocols: false in the project config). As a result, the subsection “Protocol Consolidation” (page 326) becomes redundant. With new Elixir you don’t need to worry about consolidation.

Embedded build and permanent applications

This change has been introduced way back in Elixir 1.0.4, and there’s a nice post by José Valim on the subject.

The gist of the story is that two mix properties are introduced which allow you to configure the “embedded build” and “permanent applications”. By default, new projects generated with Elixir 1.0.4+ will have these properties set to true for prod mix environment. If you generated your project before 1.0.4, you should add the following options to your mix.exs (in the project/0):

def project do
  [
    # ...
    build_embedded: Mix.env == :prod,
    start_permanent: Mix.env == :prod
  ]
end

When the :build_embedded option is set to true, the target folder will not contain symlinks. Instead, all data that needs to be in that folder (e.g. the content of the priv folder) will be copied.

The start_permanent option, if set to true, will cause the OTP application to be started as permanent. If the application crashes, that is if the top-level supervisor terminates, the whole BEAM node will be terminated. This makes sense in the production, because it allows you to to detect application crash in another OS process, and do something about it.

As José explains, it’s sensible to set both options to true for production environment. In contrast, you probably want to have them unset during development for convenience.

That’s all folks :-)

Yep, nothing else of the book content is affected by new changes to Elixir. However, many cool features have been introduced since Elixir 1.0, such as the with special form, or the mix profile.fprof task. Therefore, I suggest reading through the changelogs of recent releases :-)

Happy coding!