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<main>
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<h1><a class="header" href="#pass-variables-to-closure" id="pass-variables-to-closure">Pass variables to closure</a></h1>
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<h2><a class="header" href="#description" id="description">Description</a></h2>
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<p>By default, closures capture their environment by borrowing. Or you can use <code>move</code>-closure
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to move whole environment. However, often you want to move just some variables to closure,
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give it copy of some data, pass it by reference, or perform some other transformation.</p>
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<p>Use variable rebinding in separate scope for that.</p>
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<h2><a class="header" href="#example" id="example">Example</a></h2>
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<p>Use</p>
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<pre><pre class="playground"><code class="language-rust edition2018">
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<span class="boring">#![allow(unused)]
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</span><span class="boring">fn main() {
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</span>use std::rc::Rc;
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let num1 = Rc::new(1);
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let num2 = Rc::new(2);
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let num3 = Rc::new(3);
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let closure = {
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// `num1` is moved
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let num2 = num2.clone(); // `num2` is cloned
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let num3 = num3.as_ref(); // `num3` is borrowed
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move || {
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*num1 + *num2 + *num3;
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}
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};
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<span class="boring">}
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</span></code></pre></pre>
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<p>instead of</p>
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<pre><pre class="playground"><code class="language-rust edition2018">
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<span class="boring">#![allow(unused)]
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</span><span class="boring">fn main() {
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</span>use std::rc::Rc;
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let num1 = Rc::new(1);
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let num2 = Rc::new(2);
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let num3 = Rc::new(3);
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let num2_cloned = num2.clone();
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let num3_borrowed = num3.as_ref();
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let closure = move || {
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*num1 + *num2_cloned + *num3_borrowed;
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};
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<span class="boring">}
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</span></code></pre></pre>
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<h2><a class="header" href="#advantages" id="advantages">Advantages</a></h2>
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<p>Copied data are grouped together with closure definition, so their purpose is more clear
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and they will be dropped immediately even if they are not consumed by closure.</p>
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<p>Closure uses same variable names as surrounding code whether data are copied or moved.</p>
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<h2><a class="header" href="#disadvantages" id="disadvantages">Disadvantages</a></h2>
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<p>Additional indentation of closure body.</p>
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