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<h1 class="title">Associated Types</h1>
<p><small>There is a new edition of the book and this is an old link.</small></p>
<blockquote>
<p>Associated types are a way of associating a type placeholder with a trait such that the trait method definitions can use these placeholder types in their signatures.</p>
</blockquote>
<pre class="rust rust-example-rendered">
<span class="kw">pub</span> <span class="kw">trait</span> <span class="ident">Iterator</span> {
<span class="kw">type</span> <span class="ident">Item</span>;
<span class="kw">fn</span> <span class="ident">next</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="self">Self</span>::<span class="ident">Item</span><span class="op">></span>;
}<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Afn%20main()%20%7B%0Apub%20trait%20Iterator%20%7B%0A%20%20%20%20type%20Item%3B%0A%20%20%20%20fn%20next(%26mut%20self)%20-%3E%20Option%3CSelf%3A%3AItem%3E%3B%0A%7D%0A%7D">Run</a></pre>
<hr />
<p>Here are the relevant sections in the new and old books:</p>
<ul>
<li><strong><a href="second-edition/ch19-03-advanced-traits.html#associated-types-specify-placeholder-types-in-trait-definitions">In the second edition: Ch 19.03 — Advanced Traits</a></strong></li>
<li><small><a href="first-edition/associated-types.html">In the first edition: Ch 3.30 — Associated Types</a></small></li>
</ul>
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