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<ol class="chapter"><li class="affix"><a href="README.html">Introduction</a></li><li><a href="getting-started.html"><strong aria-hidden="true">1.</strong> Getting Started</a></li><li><a href="guessing-game.html"><strong aria-hidden="true">2.</strong> Tutorial: Guessing Game</a></li><li><a href="syntax-and-semantics.html"><strong aria-hidden="true">3.</strong> Syntax and Semantics</a></li><li><ol class="section"><li><a href="variable-bindings.html"><strong aria-hidden="true">3.1.</strong> Variable Bindings</a></li><li><a href="functions.html"><strong aria-hidden="true">3.2.</strong> Functions</a></li><li><a href="primitive-types.html"><strong aria-hidden="true">3.3.</strong> Primitive Types</a></li><li><a href="comments.html"><strong aria-hidden="true">3.4.</strong> Comments</a></li><li><a href="if.html"><strong aria-hidden="true">3.5.</strong> if</a></li><li><a href="loops.html"><strong aria-hidden="true">3.6.</strong> Loops</a></li><li><a href="vectors.html"><strong aria-hidden="true">3.7.</strong> Vectors</a></li><li><a href="ownership.html"><strong aria-hidden="true">3.8.</strong> Ownership</a></li><li><a href="references-and-borrowing.html"><strong aria-hidden="true">3.9.</strong> References and Borrowing</a></li><li><a href="lifetimes.html"><strong aria-hidden="true">3.10.</strong> Lifetimes</a></li><li><a href="mutability.html"><strong aria-hidden="true">3.11.</strong> Mutability</a></li><li><a href="structs.html"><strong aria-hidden="true">3.12.</strong> Structs</a></li><li><a href="enums.html"><strong aria-hidden="true">3.13.</strong> Enums</a></li><li><a href="match.html"><strong aria-hidden="true">3.14.</strong> Match</a></li><li><a href="patterns.html"><strong aria-hidden="true">3.15.</strong> Patterns</a></li><li><a href="method-syntax.html"><strong aria-hidden="true">3.16.</strong> Method Syntax</a></li><li><a href="strings.html"><strong aria-hidden="true">3.17.</strong> Strings</a></li><li><a href="generics.html"><strong aria-hidden="true">3.18.</strong> Generics</a></li><li><a href="traits.html"><strong aria-hidden="true">3.19.</strong> Traits</a></li><li><a href="drop.html"><strong aria-hidden="true">3.20.</strong> Drop</a></li><li><a href="if-let.html"><strong aria-hidden="true">3.21.</strong> if let</a></li><li><a href="trait-objects.html"><strong aria-hidden="true">3.22.</strong> Trait Objects</a></li><li><a href="closures.html"><strong aria-hidden="true">3.23.</strong> Closures</a></li><li><a href="ufcs.html"><strong aria-hidden="true">3.24.</strong> Universal Function Call Syntax</a></li><li><a href="crates-and-modules.html"><strong aria-hidden="true">3.25.</strong> Crates and Modules</a></li><li><a href="const-and-static.html"><strong aria-hidden="true">3.26.</strong> const and static</a></li><li><a href="attributes.html"><strong aria-hidden="true">3.27.</strong> Attributes</a></li><li><a href="type-aliases.html"><strong aria-hidden="true">3.28.</strong> type aliases</a></li><li><a href="casting-between-types.html"><strong aria-hidden="true">3.29.</strong> Casting between types</a></li><li><a href="associated-types.html"><strong aria-hidden="true">3.30.</strong> Associated Types</a></li><li><a href="unsized-types.html"><strong aria-hidden="true">3.31.</strong> Unsized Types</a></li><li><a href="operators-and-overloading.html"><strong aria-hidden="true">3.32.</strong> Operators and Overloading</a></li><li><a href="deref-coercions.html"><strong aria-hidden="true">3.33.</strong> Deref coercions</a></li><li><a href="macros.html"><strong aria-hidden="true">3.34.</strong> Macros</a></li><li><a href="raw-pointers.html"><strong aria-hidden="true">3.35.</strong> Raw Pointers</a></li><li><a href="unsafe.html"><strong aria-hidden="true">3.36.</strong> unsafe</a></li></ol></li><li><a href="effective-rust.html"><strong aria-hidden="true">4.</strong> Effective Rust</a></li><li><ol class="section"><li><a href="the-stack-and-the-heap.html"><strong aria-hidden="true">4.1.</strong> The Stack and the Heap</a></li><li><a href="testing.html"><strong aria-hidden="true">4.2.</strong> Testing</a></li><li><a href="conditional-compilation.html"><strong aria-hidden="true">4.3.</strong> Conditional Compilation</a></li><li><a href="documentation.html"><strong aria-hidden="true">4.4.</strong> Documentation</a></li><li><a href="iterators.html"><strong aria-hidden="true">4.5.</strong> Iterators</a></li><li><a href="concurrency.html"><strong aria-hidden="true">4.6.</strong> Concurrency</a></li><li><a href="error-handling.html"><strong aria-hidden="true">4.7.</strong> Error Handling</a></li><li><a href="choosing-your-guarantees.html"><strong aria-hidden="true">4.8.</strong> Choosing your Guarantees</a></li><li><a href="ffi.html"><strong aria-hidden="true">4.9.</strong> FFI</a></li><li><a href="borrow-and-asref.html"><strong aria-hidden="true">4.10.</strong> Borrow and AsRef</a></li><li><a href="release-channels.html"><strong aria-hidden="true">4.11.</strong> Release Channels</a></li><li><a href="using-rust-without-the-standard-library.html"><strong aria-hidden="true">4.12.</strong> Using Rust without the standard library</a></li><li><a href="procedural-macros.html"><strong aria-hidden="true">4.13.</strong> Procedural Macros (and custom derive)</a></li></ol></li><li><a href="glossary.html" class="active"><strong aria-hidden="true">5.</strong> Glossary</a></li><li><a href="syntax-index.html"><strong aria-hidden="true">6.</strong> Syntax Index</a></li><li><a href="bibliography.html"><strong aria-hidden="true">7.</strong> Bibliography</a></li></ol>
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<h1 class="menu-title">The Rust Programming Language</h1>
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<a class="header" href="glossary.html#glossary" id="glossary"><h1>Glossary</h1></a>
<p>Not every Rustacean has a background in systems programming, nor in computer
science, so we've added explanations of terms that might be unfamiliar.</p>
<a class="header" href="glossary.html#abstract-syntax-tree" id="abstract-syntax-tree"><h3>Abstract Syntax Tree</h3></a>
<p>When a compiler is compiling your program, it does a number of different things.
One of the things that it does is turn the text of your program into an
‘abstract syntax tree’, or ‘AST’. This tree is a representation of the structure
of your program. For example, <code>2 + 3</code> can be turned into a tree:</p>
<pre><code class="language-text"> +
/ \
2 3
</code></pre>
<p>And <code>2 + (3 * 4)</code> would look like this:</p>
<pre><code class="language-text"> +
/ \
2 *
/ \
3 4
</code></pre>
<a class="header" href="glossary.html#arity" id="arity"><h3>Arity</h3></a>
<p>Arity refers to the number of arguments a function or operation takes.</p>
<pre><pre class="playpen"><code class="language-rust">
# #![allow(unused_variables)]
#fn main() {
let x = (2, 3);
let y = (4, 6);
let z = (8, 2, 6);
#}</code></pre></pre>
<p>In the example above <code>x</code> and <code>y</code> have arity 2. <code>z</code> has arity 3.</p>
<a class="header" href="glossary.html#bounds" id="bounds"><h3>Bounds</h3></a>
<p>Bounds are constraints on a type or <a href="traits.html">trait</a>. For example, if a bound
is placed on the argument a function takes, types passed to that function
must abide by that constraint.</p>
<a class="header" href="glossary.html#combinators" id="combinators"><h3>Combinators</h3></a>
<p>Combinators are higher-order functions that apply only functions and
earlier defined combinators to provide a result from its arguments.
They can be used to manage control flow in a modular fashion.</p>
<a class="header" href="glossary.html#dst-dynamically-sized-type" id="dst-dynamically-sized-type"><h3>DST (Dynamically Sized Type)</h3></a>
<p>A type without a statically known size or alignment. (<a href="../../nomicon/exotic-sizes.html#dynamically-sized-types-dsts">more info</a>)</p>
<a class="header" href="glossary.html#expression" id="expression"><h3>Expression</h3></a>
<p>In computer programming, an expression is a combination of values, constants,
variables, operators and functions that evaluate to a single value. For example,
<code>2 + (3 * 4)</code> is an expression that returns the value 14. It is worth noting
that expressions can have side-effects. For example, a function included in an
expression might perform actions other than simply returning a value.</p>
<a class="header" href="glossary.html#expression-oriented-language" id="expression-oriented-language"><h3>Expression-Oriented Language</h3></a>
<p>In early programming languages, <a href="glossary.html#expression">expressions</a> and
<a href="glossary.html#statement">statements</a> were two separate syntactic categories: expressions had
a value and statements did things. However, later languages blurred this
distinction, allowing expressions to do things and statements to have a value.
In an expression-oriented language, (nearly) every statement is an expression
and therefore returns a value. Consequently, these expression statements can
themselves form part of larger expressions.</p>
<a class="header" href="glossary.html#statement" id="statement"><h3>Statement</h3></a>
<p>In computer programming, a statement is the smallest standalone element of a
programming language that commands a computer to perform an action.</p>
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