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<section id="dealing-with-deprecations">
<h1>Dealing With Deprecations<a class="headerlink" href="#dealing-with-deprecations" title="Permalink to this headline">#</a></h1>
<p>Deprecations are commonly used to allow APIs to evolve over time, by phasing out
no-longer-fashionable API functions and replacing them with newer, cooler
replacements. This page explains how libraries in the GNOME stack do
deprecations, and what mechanisms they provide for an application
developer—you—to deal with them.</p>
<p>One important thing to keep in mind is that deprecated does not mean broken,
or unusable. There is no need to rush into replacing every deprecated function
by its replacement right away. The next major release of the library in question
(which is the point at which deprecated API may be dropped) may be years away.
Until that happens, it is perfectly fine to keep using the functions.</p>
<section id="basics">
<h2>Basics<a class="headerlink" href="#basics" title="Permalink to this headline">#</a></h2>
<p>How does one recognize that a function is deprecated? Since a few years, the
GNOME libraries annotates deprecations in their headers, like this:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">GLIB_DEPRECATED_IN_2_26</span><span class="w"></span>
<span class="kt">void</span><span class="w"> </span><span class="n">g_completion_clear_items</span><span class="w"> </span><span class="p">(</span><span class="n">GCompletion</span><span class="o">*</span><span class="w"> </span><span class="n">cmp</span><span class="p">);</span><span class="w"></span>
<span class="n">GLIB_DEPRECATED_IN_2_40_FOR</span><span class="p">(</span><span class="n">g_settings_schema_key_get_range</span><span class="p">)</span><span class="w"></span>
<span class="n">GVariant</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">g_settings_get_range</span><span class="w"> </span><span class="p">(</span><span class="n">GSettings</span><span class="w"> </span><span class="o">*</span><span class="n">settings</span><span class="p">,</span><span class="w"></span>
<span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">gchar</span><span class="w"> </span><span class="o">*</span><span class="n">key</span><span class="p">);</span><span class="w"></span>
<span class="n">GDK_DEPRECATED_IN_3_10</span><span class="w"></span>
<span class="kt">void</span><span class="w"> </span><span class="n">gtk_window_reshow_with_initial_size</span><span class="w"> </span><span class="p">(</span><span class="n">GtkWindow</span><span class="w"> </span><span class="o">*</span><span class="n">window</span><span class="p">);</span><span class="w"></span>
</pre></div>
</div>
<p>These annotations are defined as macros in the GLib headers, which expand to
function attributes that cause the C compiler to warn when these functions are
used.</p>
<p>In addition, the doc comments for deprecated functions contain a <code class="docutils literal notranslate"><span class="pre">Deprecated:</span></code>
tag:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="cm">/**</span>
<span class="cm"> * g_completion_clear_items:</span>
<span class="cm"> * @cmp: the #GCompletion.</span>
<span class="cm"> *</span>
<span class="cm"> * Removes all items from the #GCompletion. The items are not freed, so if the</span>
<span class="cm"> * memory was dynamically allocated, it should be freed after calling this</span>
<span class="cm"> * function.</span>
<span class="cm"> *</span>
<span class="cm"> * Deprecated:2.26: Rarely used API</span>
<span class="cm"> */</span><span class="w"></span>
<span class="cm">/**</span>
<span class="cm"> * g_settings_get_range:</span>
<span class="cm"> * @settings: a #GSettings</span>
<span class="cm"> * @key: the key to query the range of</span>
<span class="cm"> *</span>
<span class="cm"> * Queries the range of a key.</span>
<span class="cm"> *</span>
<span class="cm"> * Since: 2.28</span>
<span class="cm"> *</span>
<span class="cm"> * Deprecated: 2.40: Use g_settings_schema_key_get_range() instead.</span>
<span class="cm"> */</span><span class="w"></span>
<span class="cm">/**</span>
<span class="cm"> * gtk_window_reshow_with_initial_size:</span>
<span class="cm"> * @window: a #GtkWindow</span>
<span class="cm"> *</span>
<span class="cm"> * Hides @window, then reshows it, resetting the</span>
<span class="cm"> * default size and position of the window. Used</span>
<span class="cm"> * by GUI builders only.</span>
<span class="cm"> *</span>
<span class="cm"> * Deprecated: 3.10: GUI builders can call gtk_widget_hide(),</span>
<span class="cm"> * gtk_widget_unrealize() and then gtk_widget_show() on @window</span>
<span class="cm"> * themselves, if they still need this functionality.</span>
<span class="cm"> */</span><span class="w"></span>
</pre></div>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>If you are a library maintainer: it is important that the Deprecated tag
contains not just the version in which the symbol was deprecated, but also
an explanation of how to replace the symbol with non-deprecated API, if
a replacement is possible.</p>
</div>
</section>
<section id="deprecation-warnings">
<h2>Deprecation warnings<a class="headerlink" href="#deprecation-warnings" title="Permalink to this headline">#</a></h2>
<p>Ultimatively, the <code class="docutils literal notranslate"><span class="pre">GDK_DEPRECATED_IN_3_10</span></code> macro expands to a compiler
attribute — like <code class="docutils literal notranslate"><span class="pre">__attribute__((__deprecated__))</span></code>, in GCC — which causes a
reasonably modern compiler to emit warnings when you compile your program; for
instance:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>$ make testheaderbar
CC testheaderbar.o
testheaderbar.c: In function main:
testheaderbar.c:192:3: warning: gtk_window_reshow_with_initial_size is deprecated (declared at ../gtk/gtkwindow.h:419) [-Wdeprecated-declarations]
gtk_window_reshow_with_initial_size (GTK_WINDOW (window));
^
CCLD testheaderbar
</pre></div>
</div>
<p>Note that this is just a warning: the program was still successfully built.</p>
<div class="admonition tip">
<p class="admonition-title">Tip</p>
<p>When you decide to port your code away from deprecated symbols, you can ask
the compiler to turn deprecation warnings into errors; for instance, with
GCC, you can add <code class="docutils literal notranslate"><span class="pre">-Werror=deprecated-declarations</span></code> to your compiler flags.</p>
</div>
</section>
<section id="ignoring-all-deprecation-warnings">
<h2>Ignoring all deprecation warnings<a class="headerlink" href="#ignoring-all-deprecation-warnings" title="Permalink to this headline">#</a></h2>
<p>If you want to ignore deprecation warnings you can either tell your compiler to
not emit warnings—for instance, with GCC, you can add <code class="docutils literal notranslate"><span class="pre">-Wno-deprecated-declarations</span></code>
to your compiler flags. Or you can disable deprecation warnings for the
libraries that youre using—for instance, by adding to your <code class="docutils literal notranslate"><span class="pre">meson.build</span></code> file:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">add_project_arguments</span><span class="p">([</span>
<span class="s1">&#39;-DGLIB_DISABLE_DEPRECATION_WARNINGS&#39;</span><span class="p">,</span>
<span class="s1">&#39;-DGTK_DISABLE_DEPRECATION_WARNINGS&#39;</span><span class="p">,</span>
<span class="p">],</span>
<span class="n">language</span><span class="p">:</span> <span class="s1">&#39;c&#39;</span><span class="p">,</span>
<span class="p">)</span>
</pre></div>
</div>
<p>Every library that provides deprecation annotations should also provide a way to
disable them.</p>
</section>
<section id="selectively-ignoring-deprecation-warnings">
<h2>Selectively ignoring deprecation warnings<a class="headerlink" href="#selectively-ignoring-deprecation-warnings" title="Permalink to this headline">#</a></h2>
<p>Sometimes it is impractical to avoid certain deprecated functions, even though
your code is otherwise deprecation-free. In this case, you probably dont want
to disable all deprecation warnings, and instead just selectively mark the code
sections in which the deprecated functions are used:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">G_GNUC_BEGIN_IGNORE_DEPRECATIONS</span><span class="w"></span>
<span class="nf">gtk_window_reshow_with_initial_size</span><span class="w"> </span><span class="p">(</span><span class="n">window</span><span class="p">);</span><span class="w"></span>
<span class="n">G_GNUC_END_IGNORE_DEPRECATIONS</span><span class="w"></span>
</pre></div>
</div>
</section>
<section id="targeting-specific-library-versions">
<h2>Targeting specific library versions<a class="headerlink" href="#targeting-specific-library-versions" title="Permalink to this headline">#</a></h2>
<p>If your application was developed against a certain version of a library, say
GLib 2.56, and you want to ensure that it continues to work on systems with this
version of GLib, as well as newer versions, there are two things you need to
worry about.</p>
<p>Newer versions of GLib may deprecate API that you are using. There is no reason
for you to stop using it, since it was not deprecated in 2.56 (and the
replacements will probably not be available in 2.56), but you also want to build
your application with newer versions of GLib without warnings.</p>
<p>Even if your development system has a newer version of GLib, you want avoid
using GLib API that was introduced after 2.56, to keep your application working
on systems with GLib 2.56.</p>
<p>The deprecations and API additions in the GNOME stack are versioned, which lets
you achieve these goals by defining the range of versions of the APIs that your
application is expected to work with. This is done with a pair of macros, which
are typically defined in your <code class="docutils literal notranslate"><span class="pre">meson.build</span></code> file:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">add_project_arguments</span><span class="p">([</span>
<span class="s1">&#39;-DGLIB_VERSION_MIN_REQUIRED=GLIB_VERSION_2_56&#39;</span><span class="p">,</span>
<span class="s1">&#39;-DGLIB_VERSION_MAX_ALLOWED=GLIB_VERSION_2_56&#39;</span><span class="p">,</span>
<span class="p">],</span>
<span class="n">language</span><span class="p">:</span> <span class="s1">&#39;c&#39;</span><span class="p">,</span>
<span class="p">)</span>
</pre></div>
</div>
<p>Each library has their own macros. For GLib, they are
<code class="docutils literal notranslate"><span class="pre">GLIB_VERSION_MIN_REQUIRED</span></code> and <code class="docutils literal notranslate"><span class="pre">GLIB_VERSION_MAX_ALLOWED</span></code>. For GTK, they
are <code class="docutils literal notranslate"><span class="pre">GDK_VERSION_MIN_REQUIRED</span></code> and <code class="docutils literal notranslate"><span class="pre">GDK_VERSION_MAX_ALLOWED</span></code>.</p>
<p>The definition for these macros must encode the major and minor version in a
binary format. You can either use predefined values such as <code class="docutils literal notranslate"><span class="pre">GLIB_VERSION_2_56</span></code>,
<code class="docutils literal notranslate"><span class="pre">GDK_VERSION_3_10</span></code>, or use the <code class="docutils literal notranslate"><span class="pre">G_ENCODE_VERSION</span></code> macro like this:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="cp">#define GLIB_VERSION_MIN_REQUIRED G_ENCODE_VERSION(2,56)</span>
</pre></div>
</div>
<div class="admonition important">
<p class="admonition-title">Important</p>
<p>Both the <code class="docutils literal notranslate"><span class="pre">MIN_REQUIRED</span></code> and <code class="docutils literal notranslate"><span class="pre">MAX_ALLOWED</span></code> macros must be defined
<strong>before</strong> including the header for the corresponding library.</p>
</div>
</section>
<section id="additional-references">
<h2>Additional references<a class="headerlink" href="#additional-references" title="Permalink to this headline">#</a></h2>
<ul class="simple">
<li><p><a class="reference external" href="https://docs.gtk.org/glib/compiling.html">Compiling GLib applications</a></p></li>
<li><p><a class="reference external" href="https://docs.gtk.org/gtk4/compiling.html">Compiling GTK applications</a></p></li>
</ul>
</section>
</section>
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<ul>
<li><a class="reference internal" href="#">Dealing With Deprecations</a><ul>
<li><a class="reference internal" href="#basics">Basics</a></li>
<li><a class="reference internal" href="#deprecation-warnings">Deprecation warnings</a></li>
<li><a class="reference internal" href="#ignoring-all-deprecation-warnings">Ignoring all deprecation warnings</a></li>
<li><a class="reference internal" href="#selectively-ignoring-deprecation-warnings">Selectively ignoring deprecation warnings</a></li>
<li><a class="reference internal" href="#targeting-specific-library-versions">Targeting specific library versions</a></li>
<li><a class="reference internal" href="#additional-references">Additional references</a></li>
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