Post about Erlang 17.0 and namespaced_types

_posts/2014-04-18-erlang-17-0-supporting-deprecated-types-without-removing-warnings_as_errors.md

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+---
+layout: post
+title: 'Erlang 17.0: Supporting Deprecated Types Without Removing warnings_as_errors'
+description: "Simple workaround for supporting deprecated types and warnings_as_errors."
+date: 2014-04-18 21:25:00 CEST
+category: posts
+tags: [erlang, programming, english]
+image:
+  feature: header/abstract-10.jpg
+  credit: dargadgetz
+  creditlink: http://www.dargadgetz.com/ios-7-abstract-wallpaper-pack-for-iphone-5-and-ipod-touch-retina/
+comments: true
+share: true
+---
+
+Erlang 17.0 [deprecated some pre-defined types](http://www.erlang.org/download/otp_src_17.0.readme) like `dict()` and `gb_tree()` in favor of `dict:dict()` and `gb_tree:tree()`. The workaround they suggest (`nowarn_deprecated_type`) works in 17.0, but would break once the deprecated types are removed.  
+Not using `nowarn_deprecated_type` means that you can't use `warnings_as_errors`, because it would make deprecation warnings an error.
+
+A rather nice solution to this issue an option that [rebar](https://github.com/rebar/rebar) takes: `platform_define`.
+
+>It is also possible to specify platform specific options by specifying a pair or a triplet where the first string is a regex that is checked against the string
+>
+>  OtpRelease ++ "-" ++ SysArch ++ "-" ++ Words.
+>
+>where
+>
+>  OtpRelease = erlang:system_info(otp_release).  
+>  SysArch = erlang:system_info(system_architecture).  
+>  Words = integer_to_list(8 * erlang:system_info({wordsize, external})).
+
+This allows us to set a `namespaced_types` option on 17.0+ only.
+
+{% highlight erlang %}
+{erl_opts, [
+  {platform_define, "^[0-9]+", namespaced_types},
+  debug_info,
+  warnings_as_errors
+]}.
+{% endhighlight %}
+
+In your source files you can then check if the option is set and define an (internal) type accordingly.
+
+{% highlight erlang linenos %}
+-ifdef(namespaced_types).
+-type xxx_dict() :: dict:dict().
+-else.
+-type xxx_dict() :: dict().
+-endif.
+{% endhighlight %}
+
+I learned about this trick by looking at how [meck](https://github.com/eproxus/meck) handles Erlang 17.0 support.