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<!DOCTYPE html>
<html lang="en"><head>
<script src="index_files/libs/clipboard/clipboard.min.js"></script>
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<meta name="generator" content="quarto-1.2.335">
<meta name="author" content="Bernd Doser">
<title>The New ISO Standard C++20</title>
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</head>
<body class="quarto-light">
<div class="reveal">
<div class="slides">
<section id="title-slide" class="quarto-title-block center">
<h1 class="title">The New ISO Standard C++20</h1>
<div class="quarto-title-authors">
<div class="quarto-title-author">
<div class="quarto-title-author-name">
Bernd Doser
</div>
<p class="quarto-title-affiliation">
<a href="https://h-its.org">HITS gGmbH</a>
</p>
</div>
</div>
<p class="date">July 2022</p>
</section>
<section id="this-presentation-is-available-at" class="slide level2 center">
<h2>This presentation is available at</h2>
<p><a href="https://bernddoser.github.io/workshop-cpp20">https://bernddoser.github.io/workshop-cpp20</a></p>
</section>
<section id="agenda" class="slide level2">
<h2>Agenda</h2>
<div>
<ul>
<li class="fragment">Warm-up with C++</li>
<li class="fragment">Important C++11 features</li>
<li class="fragment">C++20 features
<ul>
<li class="fragment">Concepts, ranges</li>
<li class="fragment">Modules, coroutines</li>
<li class="fragment">std::format, three-way comparison</li>
</ul></li>
<li class="fragment">Coding competition</li>
</ul>
</div>
<!-- TODO
- Modules
- Concepts
- Meta programming
- Reflections
Exercises:
- C++98 Warm-up matrix
- Smart pointer
- Move semantic
- Concepts
- Ranges
- Three-way comparison
- format
- Pancakes
-->
</section>
<section id="my-background" class="slide level2">
<h2>My Background</h2>
<div>
<ul>
<li class="fragment">PhD in theoretical chemistry
<ul>
<li class="fragment">Linear scaling electron-electron correlation</li>
</ul></li>
<li class="fragment">C++ scientific software developer since 2004</li>
<li class="fragment">Automatic differentiation for tailor-made force fields (<a href="https://avmatsim.eu/">AMS GmbH Freiburg</a>)</li>
<li class="fragment">Open source projects @ HITS: <a href="https://github.com/HITS-MBM/gromacs-fda">GROMACS-FDA</a>, <a href="https://github.com/HITS-MCM/gromacs-ramd">GROMACS-RAMD</a>, <a href="https://github.com/HITS-AIN/PINK">PINK</a>, <a href="https://emcl-gitlab.iwr.uni-heidelberg.de/hiflow3.org/hiflow3">HiFlow3</a>, <a href="https://github.com/HITS-TOS/TACO">TACO</a></li>
<li class="fragment">Personal open source projects: <a href="https://github.com/BrainTwister/BlasBooster">BlasBooster</a>, <a href="https://github.com/BrainTwister/GeneHunter">GeneHunter</a></li>
</ul>
</div>
</section>
<section id="why-c" class="slide level2">
<h2>Why C++?</h2>
<div>
<ul>
<li class="fragment">High performance</li>
<li class="fragment">Multi-paradigm
<ul>
<li class="fragment">Imperative</li>
<li class="fragment">Object-oriented</li>
<li class="fragment">Generic</li>
<li class="fragment">Functional</li>
</ul></li>
<li class="fragment">Strong type system</li>
<li class="fragment">Strict backward compatibility</li>
</ul>
</div>
</section>
<section id="iso-standardization" class="slide level2">
<h2>ISO Standardization</h2>
<ul>
<li>C++98: First ISO Standard</li>
<li>C++11: Smart pointers, move sematic, Lambda functions, range-based for loop, auto</li>
<li>C++14: Variable templates, generic lambdas</li>
<li>C++17: Structured bindings</li>
<li>C++20: Modules, concepts, coroutines, ranges</li>
<li>Suggestions for C++23: “A plan for ranges”, reflections</li>
</ul>
</section>
<section id="iso-timeline" class="slide level2">
<h2>ISO Timeline</h2>
<img data-src="images/iso-timeline.png" class="r-stretch quarto-figure-center"></section>
<section id="books-and-iso-standard" class="slide level2">
<h2>Books and ISO Standard</h2>
<div class="columns">
<div class="column" style="width:60%;">
<p><img data-src="images/book_stroustrup.jpg" class="border" width="180" height="250"> <img data-src="images/book_josuttis.jpg" class="border" width="180" height="250"> <img data-src="images/book_gottschling.jpg" class="border" width="180" height="250"> <img data-src="images/book_vandevoorde.jpg" class="border" width="180" height="250"> <img data-src="images/book_cukic.jpg" class="border" width="180" height="250"> <img data-src="images/book_grimm.jpg" class="border" width="180" height="250"></p>
</div><div class="column" style="width:40%;">
<ul>
<li>C++20 ISO Standard: ISO/IEC 14882:2020
<ul>
<li>Commercial version ~200 EUR</li>
<li><a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/n4849.pdf">Free working draft</a></li>
</ul></li>
</ul>
</div>
</div>
<aside class="notes">
<ul>
<li>Show ranges concept</li>
</ul>
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</section>
<section id="helpful-links-and-tools" class="slide level2">
<h2>Helpful Links and Tools</h2>
<div class="quarto-layout-panel">
<div class="quarto-layout-row quarto-layout-valign-top">
<div class="quarto-layout-cell" style="flex-basis: 50.0%;justify-content: center;">
<ul>
<li><a href="https://cppreference.com">cppreference.com</a></li>
<li><a href="https://gcc.godbolt.org">CompilerExplorer</a></li>
<li><a href="https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines">C++ Core Guidelines</a></li>
<li><a href="https://oleksandrkvl.github.io/2021/04/02/cpp-20-overview.html">Overview C++20 by Oleksandr Koval</a></li>
</ul>
</div>
<div class="quarto-layout-cell" style="flex-basis: 50.0%;justify-content: center;">
<p><img data-src="images/compiler_explorer.png"></p>
</div>
</div>
</div>
<aside class="notes">
<ul>
<li>Compiler feature support with proposals</li>
<li>Explain CompilerExplorer</li>
<li>Show C++ Guidlines (best practice)</li>
</ul>
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</section>
<section id="c98-warm-up" class="slide level2">
<h2>C++98 Warm-up</h2>
<div class="sourceCode" id="cb1"><pre class="sourceCode numberSource cpp number-lines code-with-copy"><code class="sourceCode cpp"><span id="cb1-1"><a href="#cb1-1"></a><span class="kw">class</span> Matrix</span>
<span id="cb1-2"><a href="#cb1-2"></a><span class="op">{</span></span>
<span id="cb1-3"><a href="#cb1-3"></a><span class="kw">public</span><span class="op">:</span></span>
<span id="cb1-4"><a href="#cb1-4"></a></span>
<span id="cb1-5"><a href="#cb1-5"></a> Matrix<span class="op">(</span><span class="dt">int</span> m<span class="op">,</span> <span class="dt">int</span> n<span class="op">)</span></span>
<span id="cb1-6"><a href="#cb1-6"></a> <span class="op">:</span> m<span class="op">(</span>m<span class="op">),</span> n<span class="op">(</span>n<span class="op">),</span> mat<span class="op">(</span>m<span class="op">*</span>n<span class="op">)</span></span>
<span id="cb1-7"><a href="#cb1-7"></a> <span class="op">{}</span></span>
<span id="cb1-8"><a href="#cb1-8"></a></span>
<span id="cb1-9"><a href="#cb1-9"></a> Matrix <span class="kw">operator</span> <span class="op">*</span> <span class="op">(</span>Matrix B<span class="op">)</span> <span class="op">{</span></span>
<span id="cb1-10"><a href="#cb1-10"></a> Matrix C<span class="op">(</span><span class="kw">this</span><span class="op">-></span>m<span class="op">,</span> B<span class="op">.</span>n<span class="op">);</span></span>
<span id="cb1-11"><a href="#cb1-11"></a> <span class="co">/* C(i,j) = sum_k A(i,k) * B(k,j) */</span></span>
<span id="cb1-12"><a href="#cb1-12"></a> <span class="cf">return</span> C<span class="op">;</span></span>
<span id="cb1-13"><a href="#cb1-13"></a> <span class="op">}</span></span>
<span id="cb1-14"><a href="#cb1-14"></a></span>
<span id="cb1-15"><a href="#cb1-15"></a><span class="kw">private</span><span class="op">:</span></span>
<span id="cb1-16"><a href="#cb1-16"></a> <span class="dt">int</span> m<span class="op">,</span>n<span class="op">;</span></span>
<span id="cb1-17"><a href="#cb1-17"></a> <span class="bu">std::</span>vector<span class="op"><</span><span class="dt">double</span><span class="op">></span> mat<span class="op">;</span></span>
<span id="cb1-18"><a href="#cb1-18"></a><span class="op">};</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
<p><a href="https://godbolt.org/z/cbbEbYcr9"><img data-src="images/godbolt-icon.svg" height="40"> Task: Find the performance issue.</a></p>
</section>
<section id="carbage-collection-vs.-raii" class="slide level2">
<h2>Carbage Collection vs. RAII</h2>
<div class="callout callout-note no-icon callout-captioned callout-style-default">
<div class="callout-body">
<div class="callout-caption">
<p><strong>Carbage Collection (Java, Python, Go)</strong></p>
</div>
<div class="callout-content">
<ul>
<li>Automatic memory management, which periodically stops all threads and frees unreferenced memory.</li>
<li>Extra overhead</li>
</ul>
</div>
</div>
</div>
<div class="callout callout-note no-icon callout-captioned callout-style-default">
<div class="callout-body">
<div class="callout-caption">
<p><strong>RAII: Resource Aquisition is Initialization (C++, Rust)</strong></p>
</div>
<div class="callout-content">
<ul>
<li>The lifetime of a resource will be bound to the lifetime of a local variable. C++ automatically manages the lifetime of locals.</li>
<li>Smart pointers (C++11) overcome the manually memory deallocation.</li>
</ul>
<p>C++ principle: “Don’t pay for something you don’t use.”</p>
</div>
</div>
</div>
</section>
<section id="raw-pointers-before-c11" class="slide level2">
<h2>Raw pointers (before C++11)</h2>
<ul>
<li>Manual allocation and deallocation of memory
<ul>
<li>Segmentation faults</li>
<li>Memory leaks</li>
</ul></li>
</ul>
<div class="sourceCode" id="cb2"><pre class="sourceCode numberSource cpp number-lines code-with-copy"><code class="sourceCode cpp"><span id="cb2-1"><a href="#cb2-1"></a><span class="dt">void</span> func<span class="op">()</span></span>
<span id="cb2-2"><a href="#cb2-2"></a><span class="op">{</span></span>
<span id="cb2-3"><a href="#cb2-3"></a> <span class="dt">int</span><span class="op">*</span> valuePtr <span class="op">=</span> <span class="kw">new</span> <span class="dt">int</span><span class="op">(</span><span class="dv">42</span><span class="op">);</span></span>
<span id="cb2-4"><a href="#cb2-4"></a> <span class="cf">if</span> <span class="op">(</span> <span class="co">/* ... */</span> <span class="op">)</span> <span class="cf">return</span><span class="op">;</span> <span class="co">// memory leak</span></span>
<span id="cb2-5"><a href="#cb2-5"></a> <span class="kw">delete</span> valuePtr<span class="op">;</span></span>
<span id="cb2-6"><a href="#cb2-6"></a><span class="op">}</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
<div class="callout callout-note callout-captioned callout-style-default">
<div class="callout-body">
<div class="callout-caption">
<div class="callout-icon-container">
<i class="callout-icon"></i>
</div>
<p><strong>Note</strong></p>
</div>
<div class="callout-content">
<p>Raw pointers (<code>new</code>) are deprecated in C++20 and will be removed in C++23.</p>
</div>
</div>
</div>
</section>
<section id="smart-pointers-c11" class="slide level2">
<h2>Smart pointers (C++11)</h2>
<div class="sourceCode" id="cb3"><pre class="sourceCode numberSource cpp number-lines code-with-copy"><code class="sourceCode cpp"><span id="cb3-1"><a href="#cb3-1"></a><span class="pp">#include </span><span class="im"><memory></span></span>
<span id="cb3-2"><a href="#cb3-2"></a></span>
<span id="cb3-3"><a href="#cb3-3"></a><span class="dt">void</span> func<span class="op">()</span></span>
<span id="cb3-4"><a href="#cb3-4"></a><span class="op">{</span></span>
<span id="cb3-5"><a href="#cb3-5"></a> <span class="bu">std::</span>shared_ptr<span class="op"><</span><span class="dt">int</span><span class="op">></span> ptr <span class="op">(</span><span class="kw">new</span> <span class="dt">int</span><span class="op">(</span><span class="dv">42</span><span class="op">));</span></span>
<span id="cb3-6"><a href="#cb3-6"></a></span>
<span id="cb3-7"><a href="#cb3-7"></a> <span class="cf">if</span> <span class="op">(</span> <span class="co">/* ... */</span> <span class="op">)</span></span>
<span id="cb3-8"><a href="#cb3-8"></a> <span class="cf">return</span><span class="op">;</span> <span class="co">// no memory leak</span></span>
<span id="cb3-9"><a href="#cb3-9"></a><span class="op">}</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
<p>Better:</p>
<div class="sourceCode" id="cb4"><pre class="sourceCode numberSource cpp number-lines code-with-copy"><code class="sourceCode cpp"><span id="cb4-1"><a href="#cb4-1"></a><span class="bu">std::</span>shared_ptr<span class="op"><</span><span class="dt">int</span><span class="op">></span> ptr <span class="op">=</span> <span class="bu">std::</span>make_shared<span class="op"><</span><span class="dt">int</span><span class="op">>();</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
<p>Best:</p>
<div class="sourceCode" id="cb5"><pre class="sourceCode numberSource cpp number-lines code-with-copy"><code class="sourceCode cpp"><span id="cb5-1"><a href="#cb5-1"></a><span class="kw">auto</span> ptr <span class="op">=</span> <span class="bu">std::</span>make_shared<span class="op"><</span><span class="dt">int</span><span class="op">>();</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
</section>
<section id="smart-pointers-c11-1" class="slide level2">
<h2>Smart pointers (C++11)</h2>
<div class="callout callout-note no-icon callout-captioned callout-style-default">
<div class="callout-body">
<div class="callout-caption">
<p><strong><code>std::unique_ptr<T></code></strong></p>
</div>
<div class="callout-content">
<ul>
<li>Allows exactly one owner of the underlying pointer</li>
<li>Can be moved to a new owner, but not copied or shared</li>
</ul>
</div>
</div>
</div>
<div class="callout callout-note no-icon callout-captioned callout-style-default">
<div class="callout-body">
<div class="callout-caption">
<p><strong><code>std::shared_ptr<T></code></strong></p>
</div>
<div class="callout-content">
<ul>
<li>Reference-counted smart pointer</li>
<li>The raw pointer is not deleted until all owners have gone out of scope</li>
</ul>
</div>
</div>
</div>
<div class="callout callout-note no-icon callout-captioned callout-style-default">
<div class="callout-body">
<div class="callout-caption">
<p><strong><code>std::weak_ptr<T></code></strong></p>
</div>
<div class="callout-content">
<ul>
<li>Required to break circular references between <code>shared_ptr</code></li>
</ul>
</div>
</div>
</div>
</section>
<section id="smart-pointers-c11-2" class="slide level2">
<h2>Smart pointers (C++11)</h2>
<div class="sourceCode" id="cb6" data-code-line-numbers="1-4|6-10|1,12-17"><pre class="sourceCode numberSource cpp number-lines code-with-copy"><code class="sourceCode cpp"><span id="cb6-1"><a href="#cb6-1"></a> <span class="kw">auto</span> p1 <span class="op">=</span> <span class="bu">std::</span>make_shared<span class="op"><</span><span class="dt">int</span><span class="op">>(</span><span class="dv">1</span><span class="op">);</span></span>
<span id="cb6-2"><a href="#cb6-2"></a> <span class="kw">auto</span> p2 <span class="op">=</span> p1<span class="op">;</span></span>
<span id="cb6-3"><a href="#cb6-3"></a> <span class="ot">assert</span><span class="op">(*</span>p2 <span class="op">==</span> <span class="dv">1</span><span class="op">);</span></span>
<span id="cb6-4"><a href="#cb6-4"></a> <span class="ot">assert</span><span class="op">(</span>p1<span class="op">.</span>use_count<span class="op">()</span> <span class="op">==</span> <span class="dv">2</span><span class="op">);</span></span>
<span id="cb6-5"><a href="#cb6-5"></a></span>
<span id="cb6-6"><a href="#cb6-6"></a> <span class="kw">auto</span> p3 <span class="op">=</span> <span class="bu">std::</span>make_unique<span class="op"><</span><span class="dt">int</span><span class="op">>(</span><span class="dv">2</span><span class="op">);</span></span>
<span id="cb6-7"><a href="#cb6-7"></a> <span class="co">// auto p4 = p3; // unique_ptr can't be copied</span></span>
<span id="cb6-8"><a href="#cb6-8"></a> <span class="kw">auto</span> p5 <span class="op">=</span> <span class="bu">std::</span>move<span class="op">(</span>p3<span class="op">);</span></span>
<span id="cb6-9"><a href="#cb6-9"></a> <span class="ot">assert</span><span class="op">(*</span>p5 <span class="op">==</span> <span class="dv">2</span><span class="op">);</span></span>
<span id="cb6-10"><a href="#cb6-10"></a> <span class="ot">assert</span><span class="op">(</span>p3 <span class="op">==</span> <span class="kw">nullptr</span><span class="op">);</span></span>
<span id="cb6-11"><a href="#cb6-11"></a></span>
<span id="cb6-12"><a href="#cb6-12"></a> <span class="co">// auto p6 = std::weak_ptr<int>(3); // weak_ptr can't own</span></span>
<span id="cb6-13"><a href="#cb6-13"></a> <span class="kw">auto</span> p6 <span class="op">=</span> <span class="bu">std::</span>weak_ptr<span class="op"><</span><span class="dt">int</span><span class="op">>(</span>p1<span class="op">);</span></span>
<span id="cb6-14"><a href="#cb6-14"></a> <span class="ot">assert</span><span class="op">(</span>p6<span class="op">.</span>use_count<span class="op">()</span> <span class="op">==</span> <span class="dv">2</span><span class="op">);</span></span>
<span id="cb6-15"><a href="#cb6-15"></a> p1<span class="op">.</span>reset<span class="op">();</span></span>
<span id="cb6-16"><a href="#cb6-16"></a> p2<span class="op">.</span>reset<span class="op">();</span></span>
<span id="cb6-17"><a href="#cb6-17"></a> <span class="ot">assert</span><span class="op">(</span>p6<span class="op">.</span>expired<span class="op">());</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
<p><a href="https://godbolt.org/z/dErqbrYM4"><img data-src="images/godbolt-icon.svg" height="40"> Exercise</a></p>
</section>
<section id="move-semantics-c11" class="slide level2">
<h2>Move Semantics (C++11)</h2>
<div class="callout callout-tip no-icon callout-captioned callout-style-default">
<div class="callout-body">
<div class="callout-caption">
<p><strong>L-values will be copied</strong></p>
</div>
<div class="callout-content">
<ul>
<li>Permanent objects with a name and a storage address</li>
<li>Copy is expensive</li>
</ul>
</div>
</div>
</div>
<div class="callout callout-tip no-icon callout-captioned callout-style-default">
<div class="callout-body">
<div class="callout-caption">
<p><strong>R-values will be moved</strong></p>
</div>
<div class="callout-content">
<ul>
<li>Temporary objects without a name and a storage address</li>
<li>R-values can only appear on the right side in an assignment</li>
<li>Move is fast</li>
</ul>
</div>
</div>
</div>
<p><a href="https://godbolt.org/z/x737PaMjK"><img data-src="images/godbolt-icon.svg" height="40"> Exersice</a></p>
</section>
<section id="containers" class="slide level2">
<h2>Containers</h2>
<table>
<thead>
<tr class="header">
<th>Name</th>
<th>Description</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td><code>array</code></td>
<td>static contiguous array</td>
</tr>
<tr class="even">
<td><code>vector</code></td>
<td>dynamic contiguous array</td>
</tr>
<tr class="odd">
<td><code>list</code></td>
<td>linked list</td>
</tr>
<tr class="even">
<td><code>set</code></td>
<td>sorted collection of unique keys</td>
</tr>
<tr class="odd">
<td><code>map</code></td>
<td>sorted collection of key-value pairs</td>
</tr>
<tr class="even">
<td><code>unordered_set</code></td>
<td>hashed collection of unique keys</td>
</tr>
<tr class="odd">
<td><code>unordered_map</code></td>
<td>hashed collection of key-value pairs</td>
</tr>
</tbody>
</table>
</section>
<section id="c20-new-keywords" class="slide level2">
<h2>C++20: New Keywords</h2>
<div class="columns">
<div class="column" style="width:50%;">
<ul>
<li>Concepts
<ul>
<li><code>concept</code></li>
<li><code>requires</code></li>
</ul></li>
<li>Coroutines
<ul>
<li><code>co_await</code></li>
<li><code>co_return</code></li>
<li><code>co_yield</code></li>
</ul></li>
</ul>
</div><div class="column" style="width:50%;">
<ul>
<li>Modules
<ul>
<li><code>import</code></li>
<li><code>module</code></li>
</ul></li>
<li>Others
<ul>
<li><code>constinit</code></li>
<li><code>consteval</code></li>
<li><code>char8_t</code></li>
</ul></li>
</ul>
</div>
</div>
</section>
<section id="modules" class="slide level2">
<h2>Modules</h2>
<ul>
<li>Modules are a new way to organize C++ code into logical components</li>
<li>Problems of the obsolete header files
<ul>
<li>Repetitive compilation of the same code</li>
<li>Inclusion order-dependent headers</li>
<li>Cyclic dependencies</li>
<li>Macros leakage in and out from headers</li>
<li>Poor encapsulation of implementation details</li>
</ul></li>
</ul>
</section>
<section id="modules-1" class="slide level2">
<h2>Modules</h2>
<div class="sourceCode" id="cb7"><pre class="sourceCode numberSource cpp number-lines code-with-copy"><code class="sourceCode cpp"><span id="cb7-1"><a href="#cb7-1"></a><span class="co">// math.cppm</span></span>
<span id="cb7-2"><a href="#cb7-2"></a><span class="kw">export</span> <span class="kw">module</span> math<span class="op">;</span></span>
<span id="cb7-3"><a href="#cb7-3"></a></span>
<span id="cb7-4"><a href="#cb7-4"></a><span class="kw">export</span> <span class="dt">int</span> add<span class="op">(</span><span class="dt">int</span> fir<span class="op">,</span> <span class="dt">int</span> sec<span class="op">)</span></span>
<span id="cb7-5"><a href="#cb7-5"></a><span class="op">{</span></span>
<span id="cb7-6"><a href="#cb7-6"></a> <span class="cf">return</span> fir <span class="op">+</span> sec<span class="op">;</span></span>
<span id="cb7-7"><a href="#cb7-7"></a><span class="op">}</span></span>
<span id="cb7-8"><a href="#cb7-8"></a></span>
<span id="cb7-9"><a href="#cb7-9"></a><span class="co">// client.cpp</span></span>
<span id="cb7-10"><a href="#cb7-10"></a><span class="kw">import</span> math<span class="op">;</span></span>
<span id="cb7-11"><a href="#cb7-11"></a></span>
<span id="cb7-12"><a href="#cb7-12"></a><span class="dt">int</span> main<span class="op">()</span></span>
<span id="cb7-13"><a href="#cb7-13"></a><span class="op">{</span></span>
<span id="cb7-14"><a href="#cb7-14"></a> add<span class="op">(</span><span class="dv">2000</span><span class="op">,</span> <span class="dv">20</span><span class="op">);</span></span>
<span id="cb7-15"><a href="#cb7-15"></a><span class="op">}</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
<ul>
<li>Modules are orthogonal to namespaces.</li>
</ul>
</section>
<section id="coroutines-evolution-of-functions" class="slide level2">
<h2>Coroutines: Evolution of Functions</h2>
<div class="sourceCode" id="cb8"><pre class="sourceCode numberSource cpp number-lines code-with-copy"><code class="sourceCode cpp"><span id="cb8-1"><a href="#cb8-1"></a><span class="dt">int</span> f1<span class="op">()</span> <span class="op">{</span> <span class="cf">return</span> <span class="dv">1</span><span class="op">;</span> <span class="op">}</span> <span class="co">// A C-like function</span></span>
<span id="cb8-2"><a href="#cb8-2"></a></span>
<span id="cb8-3"><a href="#cb8-3"></a><span class="dt">int</span> f2<span class="op">(</span><span class="dt">int</span> arg<span class="op">)</span> <span class="op">{</span> <span class="cf">return</span> arg<span class="op">;</span> <span class="op">}</span> <span class="co">// Function overloading</span></span>
<span id="cb8-4"><a href="#cb8-4"></a><span class="dt">double</span> f2<span class="op">(</span><span class="dt">double</span> arg<span class="op">)</span> <span class="op">{</span> <span class="cf">return</span> arg<span class="op">;</span> <span class="op">}</span></span>
<span id="cb8-5"><a href="#cb8-5"></a></span>
<span id="cb8-6"><a href="#cb8-6"></a><span class="kw">template</span> <span class="op"><</span><span class="kw">typename</span> T<span class="op">></span> <span class="co">// Function template</span></span>
<span id="cb8-7"><a href="#cb8-7"></a>T f3<span class="op">(</span>T arg<span class="op">)</span> <span class="op">{</span> <span class="cf">return</span> arg<span class="op">;</span> <span class="op">}</span></span>
<span id="cb8-8"><a href="#cb8-8"></a></span>
<span id="cb8-9"><a href="#cb8-9"></a><span class="kw">struct</span> F4 <span class="op">{</span> <span class="co">// Functor</span></span>
<span id="cb8-10"><a href="#cb8-10"></a> <span class="dt">int</span> <span class="kw">operator</span><span class="op">()()</span> <span class="op">{</span> <span class="cf">return</span> <span class="dv">4</span><span class="op">;</span> <span class="op">}</span></span>
<span id="cb8-11"><a href="#cb8-11"></a><span class="op">};</span></span>
<span id="cb8-12"><a href="#cb8-12"></a></span>
<span id="cb8-13"><a href="#cb8-13"></a><span class="kw">auto</span> f5 <span class="op">=</span> <span class="op">[]</span> <span class="op">(</span><span class="dt">int</span> i<span class="op">)</span> <span class="op">{</span> <span class="cf">return</span> i <span class="op">*</span> i<span class="op">;</span> <span class="op">};</span> <span class="co">// Lambda (C++11)</span></span>
<span id="cb8-14"><a href="#cb8-14"></a></span>
<span id="cb8-15"><a href="#cb8-15"></a><span class="kw">auto</span> f6 <span class="op">=</span> <span class="op">[]</span> <span class="op">(</span><span class="kw">auto</span> arg<span class="op">)</span> <span class="op">{</span> <span class="co">// Generic lambda (C++14)</span></span>
<span id="cb8-16"><a href="#cb8-16"></a> <span class="cf">return</span> <span class="bu">std::</span>to_string<span class="op">(</span>arg<span class="op">);</span></span>
<span id="cb8-17"><a href="#cb8-17"></a><span class="op">};</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
</section>
<section id="coroutines" class="slide level2">
<h2>Coroutines</h2>
<ul>
<li>A coroutine is a generalisation of a function that allows the function to be suspended and then later resumed.</li>
<li>A coroutine is stackless: their state is stored in heap, not on stack</li>
<li>A coroutine contains one of these keywords:
<ul>
<li><code>co_return</code> (coroutine return statement)</li>
<li><code>co_await</code> (await expression)</li>
<li><code>co_yield</code> (yield expression)</li>
</ul></li>
</ul>
</section>
<section id="coroutines-cppcoro" class="slide level2">
<h2>Coroutines: CppCoro</h2>
<ul>
<li>Coroutines provides a very low-level interface.</li>
<li><a href="https://github.com/lewissbaker/cppcoro">CppCoro</a> provides asynchronous programming abstractions (maybe in C++23)
<ul>
<li><code>Task<T></code>: asynchronous computation that is executed lazily</li>
<li><code>Generator<T></code>: a coroutine type that produces a sequence of values of type <code>T</code> where values are produced lazily and synchronously.</li>
</ul></li>
</ul>
</section>
<section id="coroutines-generator" class="slide level2">
<h2>Coroutines: Generator</h2>
<div class="sourceCode" id="cb9"><pre class="sourceCode numberSource cpp number-lines code-with-copy"><code class="sourceCode cpp"><span id="cb9-1"><a href="#cb9-1"></a>Generator<span class="op"><</span><span class="dt">int</span><span class="op">></span> getNext<span class="op">(</span><span class="dt">int</span> start <span class="op">=</span> <span class="dv">0</span><span class="op">,</span> <span class="dt">int</span> step <span class="op">=</span> <span class="dv">1</span><span class="op">)</span> <span class="op">{</span></span>
<span id="cb9-2"><a href="#cb9-2"></a> <span class="kw">auto</span> value <span class="op">=</span> start<span class="op">;</span></span>
<span id="cb9-3"><a href="#cb9-3"></a> <span class="cf">while</span> <span class="op">(</span><span class="kw">true</span><span class="op">)</span> <span class="op">{</span></span>
<span id="cb9-4"><a href="#cb9-4"></a> <span class="cf">co_yield</span> value<span class="op">;</span></span>
<span id="cb9-5"><a href="#cb9-5"></a> value <span class="op">+=</span> step<span class="op">;</span></span>
<span id="cb9-6"><a href="#cb9-6"></a> <span class="op">}</span></span>
<span id="cb9-7"><a href="#cb9-7"></a><span class="op">}</span></span>
<span id="cb9-8"><a href="#cb9-8"></a></span>
<span id="cb9-9"><a href="#cb9-9"></a><span class="kw">auto</span> gen <span class="op">=</span> getNext<span class="op">(</span><span class="dv">100</span><span class="op">,</span> <span class="op">-</span><span class="dv">10</span><span class="op">);</span></span>
<span id="cb9-10"><a href="#cb9-10"></a><span class="cf">for</span> <span class="op">(</span><span class="dt">int</span> i <span class="op">=</span> <span class="dv">0</span><span class="op">;</span> i <span class="op"><=</span> <span class="dv">20</span><span class="op">;</span> <span class="op">++</span>i<span class="op">)</span> <span class="op">{</span></span>
<span id="cb9-11"><a href="#cb9-11"></a> gen<span class="op">.</span>next<span class="op">();</span></span>
<span id="cb9-12"><a href="#cb9-12"></a> <span class="bu">std::</span>cout<span class="op"> <<</span> gen<span class="op">.</span>getValue<span class="op">()</span> <span class="op"><<</span> <span class="st">" "</span><span class="op">;</span></span>
<span id="cb9-13"><a href="#cb9-13"></a><span class="op">}</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
</section>
<section id="concepts" class="slide level2">
<h2>Concepts</h2>
<ul>
<li>With concepts, failure happens early and the error message is much more meaningful.</li>
<li>Before C++20 <code>enable_if</code> was used to check template arguments (<a href="https://github.com/BrainTwister/BlasBooster/blob/c1bd253971ea831f6e1b844568c2d69dfec4e239/include/BlasBooster/Core/DenseMatrix.h#L72">Example</a>).</li>
</ul>
<div class="sourceCode" id="cb10"><pre class="sourceCode numberSource cpp number-lines code-with-copy"><code class="sourceCode cpp"><span id="cb10-1"><a href="#cb10-1"></a><span class="co">// C++11</span></span>
<span id="cb10-2"><a href="#cb10-2"></a><span class="kw">template</span> <span class="op"><</span><span class="kw">typename</span> T<span class="op">></span> <span class="co">// Substitution failure is not an error (SFINAE)</span></span>
<span id="cb10-3"><a href="#cb10-3"></a><span class="bu">std::</span>enable_if_t<span class="op"><</span><span class="bu">std::</span>is_same_v<span class="op"><</span>T<span class="op">,</span> <span class="dt">int</span><span class="op">>></span> f<span class="op">(</span>T x<span class="op">);</span></span>
<span id="cb10-4"><a href="#cb10-4"></a></span>
<span id="cb10-5"><a href="#cb10-5"></a><span class="co">// C++20</span></span>
<span id="cb10-6"><a href="#cb10-6"></a><span class="dt">void</span> f<span class="op">(</span><span class="bu">std::</span>same_as<span class="op"><</span><span class="dt">int</span><span class="op">></span> <span class="kw">auto</span> x<span class="op">);</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
</section>
<section id="concepts-example" class="slide level2">
<h2>Concepts: Example</h2>
<ul>
<li>Definition</li>
</ul>
<div class="sourceCode" id="cb11"><pre class="sourceCode numberSource cpp number-lines code-with-copy"><code class="sourceCode cpp"><span id="cb11-1"><a href="#cb11-1"></a><span class="kw">template</span> <span class="op"><</span><span class="kw">typename</span> T<span class="op">></span></span>
<span id="cb11-2"><a href="#cb11-2"></a><span class="kw">concept</span> Incrementable <span class="op">=</span> <span class="kw">requires</span><span class="op">(</span>T x<span class="op">)</span> <span class="op">{</span> x<span class="op">++;</span> <span class="op">++</span>x<span class="op">;</span> <span class="op">};</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
<ul>
<li>Usage</li>
</ul>
<div class="sourceCode" id="cb12"><pre class="sourceCode numberSource cpp number-lines code-with-copy"><code class="sourceCode cpp"><span id="cb12-1"><a href="#cb12-1"></a><span class="kw">template</span> <span class="op"><</span>Incrementable T<span class="op">></span></span>
<span id="cb12-2"><a href="#cb12-2"></a><span class="dt">void</span> inc<span class="op">(</span>T t<span class="op">);</span></span>
<span id="cb12-3"><a href="#cb12-3"></a></span>
<span id="cb12-4"><a href="#cb12-4"></a><span class="kw">template</span> <span class="op"><</span>Incrementable T<span class="op">></span></span>
<span id="cb12-5"><a href="#cb12-5"></a><span class="dt">void</span> inc<span class="op">(</span>T t<span class="op">)</span> <span class="kw">requires</span> Incrementable<span class="op"><</span>T<span class="op">>;</span></span>
<span id="cb12-6"><a href="#cb12-6"></a></span>
<span id="cb12-7"><a href="#cb12-7"></a><span class="dt">void</span> inc<span class="op">(</span>Incrementable <span class="kw">auto</span> t<span class="op">);</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
</section>
<section id="the-world-before-ranges-c11" class="slide level2">
<h2>The World Before Ranges (C++11)</h2>
<div class="sourceCode" id="cb13"><pre class="sourceCode numberSource cpp number-lines code-with-copy"><code class="sourceCode cpp"><span id="cb13-1"><a href="#cb13-1"></a><span class="pp">#include </span><span class="im"><algorithm></span></span>
<span id="cb13-2"><a href="#cb13-2"></a></span>
<span id="cb13-3"><a href="#cb13-3"></a><span class="dt">int</span> main<span class="op">()</span></span>
<span id="cb13-4"><a href="#cb13-4"></a><span class="op">{</span></span>
<span id="cb13-5"><a href="#cb13-5"></a> <span class="bu">std::</span>vector<span class="op"><</span><span class="dt">int</span><span class="op">></span> data<span class="op">{</span><span class="dv">42</span><span class="op">,</span> <span class="dv">1</span><span class="op">,</span> <span class="dv">12</span><span class="op">,</span> <span class="op">-</span><span class="dv">3</span><span class="op">,</span> <span class="dv">14</span><span class="op">,</span> <span class="op">-</span><span class="dv">5</span><span class="op">};</span></span>
<span id="cb13-6"><a href="#cb13-6"></a> <span class="bu">std::</span>vector<span class="op"><</span><span class="dt">int</span><span class="op">></span> pos<span class="op">;</span></span>
<span id="cb13-7"><a href="#cb13-7"></a></span>
<span id="cb13-8"><a href="#cb13-8"></a> <span class="co">// copy only positive numbers:</span></span>
<span id="cb13-9"><a href="#cb13-9"></a> <span class="bu">std::</span>copy_if<span class="op">(</span>data<span class="op">.</span>begin<span class="op">(),</span> data<span class="op">.</span>end<span class="op">(),</span></span>
<span id="cb13-10"><a href="#cb13-10"></a> <span class="bu">std::</span>back_inserter<span class="op">(</span>pos<span class="op">),</span> <span class="op">[](</span><span class="dt">int</span> i<span class="op">){</span> <span class="cf">return</span> i <span class="op">>=</span> <span class="dv">0</span><span class="op">;</span> <span class="op">});</span></span>
<span id="cb13-11"><a href="#cb13-11"></a><span class="op">}</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
<p><a href="https://en.cppreference.com/w/cpp/algorithm/copy">cppreference std::copy_if</a></p>
<div class="sourceCode" id="cb14"><pre class="sourceCode numberSource cpp number-lines code-with-copy"><code class="sourceCode cpp"><span id="cb14-1"><a href="#cb14-1"></a><span class="kw">template</span> <span class="op"><</span><span class="kw">class</span> InputIt<span class="op">,</span> <span class="kw">class</span> OutputIt<span class="op">,</span> <span class="kw">class</span> UnaryPredicate<span class="op">></span></span>
<span id="cb14-2"><a href="#cb14-2"></a>OutputIt copy_if<span class="op">(</span> InputIt first<span class="op">,</span> InputIt last<span class="op">,</span></span>
<span id="cb14-3"><a href="#cb14-3"></a> OutputIt d_first<span class="op">,</span></span>
<span id="cb14-4"><a href="#cb14-4"></a> UnaryPredicate pred <span class="op">);</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
<p><a href="https://gcc.godbolt.org/z/7EMhaWd5q"><img data-src="images/godbolt-icon.svg" height="40"> Exercise</a></p>
</section>
<section id="ranges-what-we-want" class="slide level2">
<h2>Ranges: What We Want</h2>
<ul>
<li>Direct usage of containers without iterators (pointers)</li>
</ul>
<div class="sourceCode" id="cb15"><pre class="sourceCode numberSource cpp number-lines code-with-copy"><code class="sourceCode cpp"><span id="cb15-1"><a href="#cb15-1"></a><span class="bu">std::</span>vector<span class="op"><</span><span class="dt">int</span><span class="op">></span> v<span class="op">{</span><span class="dv">1</span><span class="op">,</span><span class="dv">2</span><span class="op">,</span><span class="dv">3</span><span class="op">};</span></span>
<span id="cb15-2"><a href="#cb15-2"></a><span class="bu">std::</span>sort<span class="op">(</span><span class="bu">std::</span>begin<span class="op">(</span>v<span class="op">),</span> <span class="bu">std::</span>end<span class="op">(</span>v<span class="op">));</span></span>
<span id="cb15-3"><a href="#cb15-3"></a><span class="bu">std::</span>ranges<span class="bu">::</span>sort<span class="op">(</span>v<span class="op">);</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
<ul>
<li>Chaining similar to unix pipes</li>
</ul>
<div class="sourceCode" id="cb16"><pre class="sourceCode numberSource cpp number-lines code-with-copy"><code class="sourceCode cpp"><span id="cb16-1"><a href="#cb16-1"></a>result <span class="op">=</span> data <span class="op">|</span> func1 <span class="op">|</span> func2 <span class="op">|</span> <span class="op">...</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
<ul>
<li>Lazy evaluation</li>
</ul>
</section>
<section id="ranges-filter" class="slide level2">
<h2>Ranges: filter</h2>
<div class="sourceCode" id="cb17"><pre class="sourceCode numberSource cpp number-lines code-with-copy"><code class="sourceCode cpp"><span id="cb17-1"><a href="#cb17-1"></a><span class="pp">#include </span><span class="im"><ranges></span></span>
<span id="cb17-2"><a href="#cb17-2"></a><span class="pp">#include </span><span class="im"><vector></span></span>
<span id="cb17-3"><a href="#cb17-3"></a></span>
<span id="cb17-4"><a href="#cb17-4"></a><span class="dt">int</span> main<span class="op">()</span></span>
<span id="cb17-5"><a href="#cb17-5"></a><span class="op">{</span></span>
<span id="cb17-6"><a href="#cb17-6"></a> <span class="bu">std::</span>vector<span class="op"><</span><span class="dt">int</span><span class="op">></span> data<span class="op">{</span><span class="dv">42</span><span class="op">,</span> <span class="dv">1</span><span class="op">,</span> <span class="dv">12</span><span class="op">,</span> <span class="op">-</span><span class="dv">3</span><span class="op">,</span> <span class="dv">14</span><span class="op">,</span> <span class="op">-</span><span class="dv">5</span><span class="op">};</span></span>
<span id="cb17-7"><a href="#cb17-7"></a> <span class="kw">auto</span> even <span class="op">=</span> <span class="op">[](</span><span class="dt">int</span> i<span class="op">){</span><span class="cf">return</span> i <span class="op">>=</span> <span class="dv">0</span><span class="op">;};</span></span>
<span id="cb17-8"><a href="#cb17-8"></a></span>
<span id="cb17-9"><a href="#cb17-9"></a> <span class="kw">auto</span> pos <span class="op">=</span> data <span class="op">|</span> <span class="bu">std::</span>views<span class="bu">::</span>filter<span class="op">(</span>even<span class="op">);</span></span>
<span id="cb17-10"><a href="#cb17-10"></a><span class="op">}</span></span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
<p><a href="https://gcc.godbolt.org/z/T5W6K46Gb"><img data-src="images/godbolt-icon.svg" height="40"> Exercise</a></p>
</section>
<section id="ranges-how-it-works" class="slide level2">
<h2>Ranges: How it works</h2>
<ul>
<li>A <code>range</code> is a concept, not a container</li>
<li>Defined in header <code><ranges></code>:</li>