<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Source to the Rust file `libcore/char/convert.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>convert.rs.html -- source</title><link rel="stylesheet" type="text/css" href="../../../normalize.css"><link rel="stylesheet" type="text/css" href="../../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../../dark.css"><link rel="stylesheet" type="text/css" href="../../../light.css" id="themeStyle"><script src="../../../storage.js"></script><link rel="shortcut icon" href="https://doc.rust-lang.org/favicon.ico"></head><body class="rustdoc source"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">☰</div><a href='../../../core/index.html'><img src='https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png' alt='logo' width='100'></a></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../../../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../../../theme.js"></script><nav class="sub"><form class="search-form js-only"><div class="search-container"><input class="search-input" name="search" autocomplete="off" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><a id="settings-menu" href="../../../settings.html"><img src="../../../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><pre class="line-numbers"><span id="1"> 1</span>
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</pre><pre class="rust ">
<span class="comment">// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT</span>
<span class="comment">// file at the top-level directory of this distribution and at</span>
<span class="comment">// http://rust-lang.org/COPYRIGHT.</span>
<span class="comment">//</span>
<span class="comment">// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or</span>
<span class="comment">// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license</span>
<span class="comment">// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your</span>
<span class="comment">// option. This file may not be copied, modified, or distributed</span>
<span class="comment">// except according to those terms.</span>
<span class="doccomment">//! Character conversions.</span>
<span class="kw">use</span> <span class="ident">convert</span>::<span class="ident">TryFrom</span>;
<span class="kw">use</span> <span class="ident">fmt</span>;
<span class="kw">use</span> <span class="ident">mem</span>::<span class="ident">transmute</span>;
<span class="kw">use</span> <span class="ident">str</span>::<span class="ident">FromStr</span>;
<span class="kw">use</span> <span class="kw">super</span>::<span class="ident">MAX</span>;
<span class="doccomment">/// Converts a `u32` to a `char`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that all [`char`]s are valid [`u32`]s, and can be cast to one with</span>
<span class="doccomment">/// [`as`]:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// let c = '💯';</span>
<span class="doccomment">/// let i = c as u32;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// assert_eq!(128175, i);</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// However, the reverse is not true: not all valid [`u32`]s are valid</span>
<span class="doccomment">/// [`char`]s. `from_u32()` will return `None` if the input is not a valid value</span>
<span class="doccomment">/// for a [`char`].</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`char`]: ../../std/primitive.char.html</span>
<span class="doccomment">/// [`u32`]: ../../std/primitive.u32.html</span>
<span class="doccomment">/// [`as`]: ../../book/first-edition/casting-between-types.html#as</span>
<span class="doccomment">///</span>
<span class="doccomment">/// For an unsafe version of this function which ignores these checks, see</span>
<span class="doccomment">/// [`from_u32_unchecked`].</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`from_u32_unchecked`]: fn.from_u32_unchecked.html</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Basic usage:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use std::char;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let c = char::from_u32(0x2764);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// assert_eq!(Some('❤'), c);</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returning `None` when the input is not a valid [`char`]:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use std::char;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let c = char::from_u32(0x110000);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// assert_eq!(None, c);</span>
<span class="doccomment">/// ```</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">from_u32</span>(<span class="ident">i</span>: <span class="ident">u32</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">char</span><span class="op">></span> {
<span class="ident">char</span>::<span class="ident">try_from</span>(<span class="ident">i</span>).<span class="ident">ok</span>()
}
<span class="doccomment">/// Converts a `u32` to a `char`, ignoring validity.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that all [`char`]s are valid [`u32`]s, and can be cast to one with</span>
<span class="doccomment">/// [`as`]:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// let c = '💯';</span>
<span class="doccomment">/// let i = c as u32;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// assert_eq!(128175, i);</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// However, the reverse is not true: not all valid [`u32`]s are valid</span>
<span class="doccomment">/// [`char`]s. `from_u32_unchecked()` will ignore this, and blindly cast to</span>
<span class="doccomment">/// [`char`], possibly creating an invalid one.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`char`]: ../../std/primitive.char.html</span>
<span class="doccomment">/// [`u32`]: ../../std/primitive.u32.html</span>
<span class="doccomment">/// [`as`]: ../../book/first-edition/casting-between-types.html#as</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function is unsafe, as it may construct invalid `char` values.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// For a safe version of this function, see the [`from_u32`] function.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`from_u32`]: fn.from_u32.html</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Basic usage:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use std::char;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let c = unsafe { char::from_u32_unchecked(0x2764) };</span>
<span class="doccomment">///</span>
<span class="doccomment">/// assert_eq!('❤', c);</span>
<span class="doccomment">/// ```</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"char_from_unchecked"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.5.0"</span>)]</span>
<span class="kw">pub</span> <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">from_u32_unchecked</span>(<span class="ident">i</span>: <span class="ident">u32</span>) <span class="op">-></span> <span class="ident">char</span> {
<span class="ident">transmute</span>(<span class="ident">i</span>)
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"char_convert"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.13.0"</span>)]</span>
<span class="kw">impl</span> <span class="ident">From</span><span class="op"><</span><span class="ident">char</span><span class="op">></span> <span class="kw">for</span> <span class="ident">u32</span> {
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">from</span>(<span class="ident">c</span>: <span class="ident">char</span>) <span class="op">-></span> <span class="self">Self</span> {
<span class="ident">c</span> <span class="kw">as</span> <span class="ident">u32</span>
}
}
<span class="doccomment">/// Maps a byte in 0x00...0xFF to a `char` whose code point has the same value, in U+0000 to U+00FF.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Unicode is designed such that this effectively decodes bytes</span>
<span class="doccomment">/// with the character encoding that IANA calls ISO-8859-1.</span>
<span class="doccomment">/// This encoding is compatible with ASCII.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that this is different from ISO/IEC 8859-1 a.k.a. ISO 8859-1 (with one less hyphen),</span>
<span class="doccomment">/// which leaves some "blanks", byte values that are not assigned to any character.</span>
<span class="doccomment">/// ISO-8859-1 (the IANA one) assigns them to the C0 and C1 control codes.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that this is *also* different from Windows-1252 a.k.a. code page 1252,</span>
<span class="doccomment">/// which is a superset ISO/IEC 8859-1 that assigns some (not all!) blanks</span>
<span class="doccomment">/// to punctuation and various Latin characters.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// To confuse things further, [on the Web](https://encoding.spec.whatwg.org/)</span>
<span class="doccomment">/// `ascii`, `iso-8859-1`, and `windows-1252` are all aliases</span>
<span class="doccomment">/// for a superset of Windows-1252 that fills the remaining blanks with corresponding</span>
<span class="doccomment">/// C0 and C1 control codes.</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"char_convert"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.13.0"</span>)]</span>
<span class="kw">impl</span> <span class="ident">From</span><span class="op"><</span><span class="ident">u8</span><span class="op">></span> <span class="kw">for</span> <span class="ident">char</span> {
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">from</span>(<span class="ident">i</span>: <span class="ident">u8</span>) <span class="op">-></span> <span class="self">Self</span> {
<span class="ident">i</span> <span class="kw">as</span> <span class="ident">char</span>
}
}
<span class="doccomment">/// An error which can be returned when parsing a char.</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"char_from_str"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.20.0"</span>)]</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">Debug</span>, <span class="ident">PartialEq</span>, <span class="ident">Eq</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">ParseCharError</span> {
<span class="ident">kind</span>: <span class="ident">CharErrorKind</span>,
}
<span class="kw">impl</span> <span class="ident">ParseCharError</span> {
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"char_error_internals"</span>,
<span class="ident">reason</span> <span class="op">=</span> <span class="string">"this method should not be available publicly"</span>,
<span class="ident">issue</span> <span class="op">=</span> <span class="string">"0"</span>)]</span>
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">hidden</span>)]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">__description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">kind</span> {
<span class="ident">CharErrorKind</span>::<span class="ident">EmptyString</span> <span class="op">=></span> {
<span class="string">"cannot parse char from empty string"</span>
},
<span class="ident">CharErrorKind</span>::<span class="ident">TooManyChars</span> <span class="op">=></span> <span class="string">"too many characters in string"</span>
}
}
}
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Copy</span>, <span class="ident">Clone</span>, <span class="ident">Debug</span>, <span class="ident">PartialEq</span>, <span class="ident">Eq</span>)]</span>
<span class="kw">enum</span> <span class="ident">CharErrorKind</span> {
<span class="ident">EmptyString</span>,
<span class="ident">TooManyChars</span>,
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"char_from_str"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.20.0"</span>)]</span>
<span class="kw">impl</span> <span class="ident">fmt</span>::<span class="ident">Display</span> <span class="kw">for</span> <span class="ident">ParseCharError</span> {
<span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-></span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
<span class="self">self</span>.<span class="ident">__description</span>().<span class="ident">fmt</span>(<span class="ident">f</span>)
}
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"char_from_str"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.20.0"</span>)]</span>
<span class="kw">impl</span> <span class="ident">FromStr</span> <span class="kw">for</span> <span class="ident">char</span> {
<span class="kw">type</span> <span class="prelude-val">Err</span> <span class="op">=</span> <span class="ident">ParseCharError</span>;
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">from_str</span>(<span class="ident">s</span>: <span class="kw-2">&</span><span class="ident">str</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="self">Self</span>, <span class="self">Self</span>::<span class="prelude-val">Err</span><span class="op">></span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">chars</span> <span class="op">=</span> <span class="ident">s</span>.<span class="ident">chars</span>();
<span class="kw">match</span> (<span class="ident">chars</span>.<span class="ident">next</span>(), <span class="ident">chars</span>.<span class="ident">next</span>()) {
(<span class="prelude-val">None</span>, <span class="kw">_</span>) <span class="op">=></span> {
<span class="prelude-val">Err</span>(<span class="ident">ParseCharError</span> { <span class="ident">kind</span>: <span class="ident">CharErrorKind</span>::<span class="ident">EmptyString</span> })
},
(<span class="prelude-val">Some</span>(<span class="ident">c</span>), <span class="prelude-val">None</span>) <span class="op">=></span> <span class="prelude-val">Ok</span>(<span class="ident">c</span>),
<span class="kw">_</span> <span class="op">=></span> {
<span class="prelude-val">Err</span>(<span class="ident">ParseCharError</span> { <span class="ident">kind</span>: <span class="ident">CharErrorKind</span>::<span class="ident">TooManyChars</span> })
}
}
}
}
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_from"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"33417"</span>)]</span>
<span class="kw">impl</span> <span class="ident">TryFrom</span><span class="op"><</span><span class="ident">u32</span><span class="op">></span> <span class="kw">for</span> <span class="ident">char</span> {
<span class="kw">type</span> <span class="ident">Error</span> <span class="op">=</span> <span class="ident">CharTryFromError</span>;
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">try_from</span>(<span class="ident">i</span>: <span class="ident">u32</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="self">Self</span>, <span class="self">Self</span>::<span class="ident">Error</span><span class="op">></span> {
<span class="kw">if</span> (<span class="ident">i</span> <span class="op">></span> <span class="ident">MAX</span> <span class="kw">as</span> <span class="ident">u32</span>) <span class="op">||</span> (<span class="ident">i</span> <span class="op">>=</span> <span class="number">0xD800</span> <span class="op">&&</span> <span class="ident">i</span> <span class="op"><=</span> <span class="number">0xDFFF</span>) {
<span class="prelude-val">Err</span>(<span class="ident">CharTryFromError</span>(()))
} <span class="kw">else</span> {
<span class="prelude-val">Ok</span>(<span class="kw">unsafe</span> { <span class="ident">from_u32_unchecked</span>(<span class="ident">i</span>) })
}
}
}
<span class="doccomment">/// The error type returned when a conversion from u32 to char fails.</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_from"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"33417"</span>)]</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Copy</span>, <span class="ident">Clone</span>, <span class="ident">Debug</span>, <span class="ident">PartialEq</span>, <span class="ident">Eq</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">CharTryFromError</span>(());
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_from"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"33417"</span>)]</span>
<span class="kw">impl</span> <span class="ident">fmt</span>::<span class="ident">Display</span> <span class="kw">for</span> <span class="ident">CharTryFromError</span> {
<span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-></span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
<span class="string">"converted integer out of range for `char`"</span>.<span class="ident">fmt</span>(<span class="ident">f</span>)
}
}
<span class="doccomment">/// Converts a digit in the given radix to a `char`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// A 'radix' here is sometimes also called a 'base'. A radix of two</span>
<span class="doccomment">/// indicates a binary number, a radix of ten, decimal, and a radix of</span>
<span class="doccomment">/// sixteen, hexadecimal, to give some common values. Arbitrary</span>
<span class="doccomment">/// radices are supported.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// `from_digit()` will return `None` if the input is not a digit in</span>
<span class="doccomment">/// the given radix.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Panics</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Panics if given a radix larger than 36.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Basic usage:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use std::char;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let c = char::from_digit(4, 10);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// assert_eq!(Some('4'), c);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Decimal 11 is a single digit in base 16</span>
<span class="doccomment">/// let c = char::from_digit(11, 16);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// assert_eq!(Some('b'), c);</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returning `None` when the input is not a digit:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use std::char;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let c = char::from_digit(20, 10);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// assert_eq!(None, c);</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Passing a large radix, causing a panic:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use std::thread;</span>
<span class="doccomment">/// use std::char;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let result = thread::spawn(|| {</span>
<span class="doccomment">/// // this panics</span>
<span class="doccomment">/// let c = char::from_digit(1, 37);</span>
<span class="doccomment">/// }).join();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// assert!(result.is_err());</span>
<span class="doccomment">/// ```</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">from_digit</span>(<span class="ident">num</span>: <span class="ident">u32</span>, <span class="ident">radix</span>: <span class="ident">u32</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">char</span><span class="op">></span> {
<span class="kw">if</span> <span class="ident">radix</span> <span class="op">></span> <span class="number">36</span> {
<span class="macro">panic</span><span class="macro">!</span>(<span class="string">"from_digit: radix is too high (maximum 36)"</span>);
}
<span class="kw">if</span> <span class="ident">num</span> <span class="op"><</span> <span class="ident">radix</span> {
<span class="kw">let</span> <span class="ident">num</span> <span class="op">=</span> <span class="ident">num</span> <span class="kw">as</span> <span class="ident">u8</span>;
<span class="kw">if</span> <span class="ident">num</span> <span class="op"><</span> <span class="number">10</span> {
<span class="prelude-val">Some</span>((<span class="string">b'0'</span> <span class="op">+</span> <span class="ident">num</span>) <span class="kw">as</span> <span class="ident">char</span>)
} <span class="kw">else</span> {
<span class="prelude-val">Some</span>((<span class="string">b'a'</span> <span class="op">+</span> <span class="ident">num</span> <span class="op">-</span> <span class="number">10</span>) <span class="kw">as</span> <span class="ident">char</span>)
}
} <span class="kw">else</span> {
<span class="prelude-val">None</span>
}
}
</pre>
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