edlang/yansi/fn.whenever.html
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<p><code>condition</code> is expected to be fast: it is checked dynamically, each time a
<a href="struct.Painted.html" title="struct yansi::Painted"><code>Painted</code></a> value is displayed.</p>
<h2 id="example"><a class="doc-anchor" href="#example">§</a>Example</h2>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>yansi::Condition;
yansi::whenever(Condition::STDOUT_IS_TTY);
<span class="comment">// On each styling, check if we have TTYs.
</span>yansi::whenever(Condition::STDOUTERR_ARE_TTY_LIVE);
<span class="comment">// Check `NO_COLOR`, `CLICOLOR`, and if we have TTYs.
</span><span class="kw">const </span>HAVE_COLOR: Condition = Condition(|| {
std::env::var_os(<span class="string">"NO_COLOR"</span>).is_none()
&amp;&amp; (Condition::CLICOLOR_LIVE)()
&amp;&amp; Condition::stdouterr_are_tty_live()
});
<span class="comment">// This will call `HAVE_COLOR` every time styling is needed. In this
// example, this means that env vars will be checked on each styling.
</span>yansi::whenever(HAVE_COLOR);
<span class="comment">// This instead caches the value (checking `env()` exactly once, now).
</span>yansi::whenever(Condition::cached((HAVE_COLOR)()));
<span class="comment">// Is identical to this:
</span><span class="kw">match </span>(HAVE_COLOR)() {
<span class="bool-val">true </span>=&gt; yansi::enable(),
<span class="bool-val">false </span>=&gt; yansi::disable(),
}</code></pre></div>
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