xmlns:its="http://www.w3.org/2005/11/its"

      type="topic"

      id="namespacing">

  <info>

    <link type="guide" xref="index#maintainer-guidelines"/>

    <credit type="author copyright">

      <name>Philip Withnall</name>

      <email its:translate="no">philip.withnall@collabora.co.uk</email>

      <years>2015, 2016</years>

    </credit>

    <include href="cc-by-sa-3-0.xml" xmlns="http://www.w3.org/2001/XInclude"/>

    <desc>

      Avoiding symbol conflicts between libraries by namespacing all APIs

    </desc>

  </info>

  <title>Namespacing</title>

  <synopsis>

    <title>Summary</title>

      If a library is namespaced correctly, it can define types and methods in

      its API which have the same names as those in another library, and a

      program can use both without conflicts. This is achieved by prefixing all

      types and method names with a namespace unique to the library.

  </synopsis>

  <section id="gobject">

    <title>GObject APIs</title>

      Consistent and complete namespacing of symbols (functions and types) and

      files is important for two key reasons:

    <list type="numbered">

      <item>

        Establishing a convention which means developers have to learn fewer

        symbol names to use the library — they can guess them reliably instead.

      
</item>

      <item>

        Ensuring symbols from two projects do not conflict if included in the

        same file.

      
</item>

    </list>

      The second point is important — imagine what would happen if every project

      exported a function called create_object(). The headers

      defining them could not be included in the same file, and even if that

      were overcome, the programmer would not know which project each function

      comes from. Namespacing eliminates these problems by using a unique,

      consistent prefix for every symbol and filename in a project, grouping

      symbols into their projects and separating them from others.

      The conventions below should be used for namespacing all symbols. They are

      <link href="https://developer.gnome.org/gobject/stable/gtype-conventions.html">

      used in all GLib-based projects</link>, so should be familiar to a lot of

      developers:

    <list>

      <item>

        Functions should use lower_case_with_underscores.

      
</item>

      <item>

        Structures, types and objects should use

        CamelCaseWithoutUnderscores.

      
</item>

      <item>

        Macros and constants should use

        UPPER_CASE_WITH_UNDERSCORES.

      
</item>

      <item>

        All symbols should be prefixed with a short (2–4 characters) version of

        the namespace. This is shortened purely for ease of typing, but should

        still be unique.

      
</item>

      <item>

        All methods of a class should also be prefixed with the class name.

      
</item>

    </list>

      Additionally, public headers should be included from a subdirectory,

      effectively namespacing the header files. For example, instead of

      #include <abc.h>, a project should allow its users to

      use #include <namespace/abc.h>.

      Some projects namespace their headers within this subdirectory — for

      example, #include <namespace/ns-abc.h> instead of

      #include <namespace/abc.h>. This is redundant, but

      harmless.

      For example, for a project called ‘Walbottle’, the short namespace ‘Wbl’

      would be chosen. If it has a ‘schema’ class and a ‘writer’ class, it

      would install headers:

    <list>

      <item>

        <file>$(includedir)/walbottle-$API_MAJOR/walbottle/schema.h</file>

      
</item>

      <item>

        <file>$(includedir)/walbottle-$API_MAJOR/walbottle/writer.h</file>

      
</item>

    </list>

      (The use of $API_MAJOR above is for

      <link xref="parallel-installability">parallel installability</link>.)

      For the schema class, the following symbols would be exported (amongst

      others), following GObject conventions:

    <list>

      <item>
WblSchema structure
</item>

      <item>
WblSchemaClass structure
</item>

      <item>
WBL_TYPE_SCHEMA macro
</item>

      <item>
WBL_IS_SCHEMA macro
</item>

      <item>
wbl_schema_get_type function
</item>

      <item>
wbl_schema_new function
</item>

      <item>
wbl_schema_load_from_data function
</item>

    </list>

  </section>

</page>