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Disabler.html
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<h1 id="disabling-parts-of-the-build">Disabling parts of the build</h1>
<p><em>This feature is available since version 0.44.0.</em></p>
<p>The following is a common fragment found in many projects:</p>
<pre><code class="language-meson">dep = dependency('foo')
# In some different directory
lib = shared_library('mylib', 'mylib.c',
dependencies : dep)
# And in a third directory
exe = executable('mytest', 'mytest.c',
link_with : lib)
test('mytest', exe)
</code></pre>
<p>This works fine but gets a bit inflexible when you want to make this
part of the build optional. Basically it reduces to adding <code>if/else</code>
statements around all target invocations. Meson provides a simpler way
of achieving the same with a disabler object.</p>
<p>A disabler object is created with the <code>disabler</code> function:</p>
<pre><code class="language-meson">d = disabler()
</code></pre>
<p>The only thing you can do to a disabler object is to ask if it has
been found:</p>
<pre><code class="language-meson">f = d.found() # returns false
</code></pre>
<p>Any other statement that uses a disabler object will immediately
return a disabler. For example assuming that <code>d</code> contains a disabler
object then</p>
<pre><code class="language-meson">d2 = some_func(d) # value of d2 will be disabler
d3 = true or d2 # value of d3 will be true because of short-circuiting
d4 = false or d2 # value of d4 will be disabler
if d # neither branch is evaluated
</code></pre>
<p>Thus to disable every target that depends on the dependency given
above, you can do something like this:</p>
<pre><code class="language-meson">if use_foo_feature
d = dependency('foo')
else
d = disabler()
endif
</code></pre>
<p>This concentrates the handling of this option in one place and other
build definition files do not need to be sprinkled with <code>if</code>
statements.</p>
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