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  7. 		<title>Clean functions</title>
    8. 

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    34. 

  34. 

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    36. 

  36. 

  37. 			<!-- Any section element inside of this container is displayed as a slide -->
    38. 

  38. 			<div class="slides">
    39. 

  39.                 <section>
    40. 

  40.                     <h2>Clean functions</h2>
    41. 

  41.                     <p>
    42. 

  42.                         Caturday will not be stopped!<br />
    43. 

  43.                         <img src="img/Willnotbestopped.gif" alt="Y U NO LOAD">
    44. 

  44.                     </p>
    45. 

  45.                 </section>
    46. 

  46. 

  47.                 <section>
    48. 

  48.                     <h2>Clean functions</h2>
    49. 

  49.                     <p>
    50. 

  50.                         Presentation by <a href="https://twitter.com/JeroenDeDauw">@JeroenDeDauw</a><br /><br />
    51. 

  51.                         bit.ly/clean-functions
    52. 

  52.                     </p>
    53. 

  53.                 </section>
    54. 

  54. 

  55.                 <section data-state="blackout">
    56. 

  56.                     <h2>Function size and naming</h2>
    57. 

  57.                 </section>
    58. 

  58. 

  59.                 <section>
    60. 

  60.                     <h3>How big should a function be?</h3>
    61. 

  61.                     <ol>
    62. 

  62.                         <li class="fragment">It should be SMALL</li>
    63. 

  63.                         <li class="fragment">It should be SMALLER than that</li>
    64. 

  64.                     </ol>
    65. 

  65.                     <br /><br />
    66. 

  66.                     <blockquote class="fragment">
    67. 

  67.                         A function should do one thing.<br />
    68. 

  68.                         It should do it well, and it should do it only.
    69. 

  69.                     </blockquote>
    70. 

  70.                 </section>
    71. 

  71. 

  72.                 <section>
    73. 

  73.                     <p>4 - 5 lines</p>
    74. 

  74.                 </section>
    75. 

  75. 

  76.                 <section>
    77. 

  77.                     <h3>What is "one thing"?</h3>
    78. 

  78.                     <p class="fragment">
    79. 

  79.                         One level of abstraction
    80. 

  80.                     </p>
    81. 

  81. 

  82.                     <pre class="fragment"><code contenteditable class="PHP">
    83. 

  83. function onFirstPost() {
    84. 

  84.     $messageText = $this->getWelcomeMessageBody();
    85. 

  85.     if ($this->addFooter()) $messageText.=$this->getWelcomeMessageFooter();
    86. 

  86.     $this->emailer->send( $messageText );
    87. 

  87.     foreach ( $this->getReviewers() as $reviewer ) {
    88. 

  88.          $this->reviewerNotifier->notify( $reviewer );
    89. 

  89.     }
    90. 

  90. }
    91. 

  91.                     </code></pre>
    92. 

  92. 

  93.                     <pre class="fragment"><code contenteditable class="PHP">
    94. 

  94. function onFirstPost() {
    95. 

  95.     $this->sendWelcomeMessage();
    96. 

  96.     $this->notifyReviewers();
    97. 

  97. }
    98. 

  98.                     </code></pre>
    99. 

  99.                 </section>
    100. 

  100. 

  101.                 <section>
    102. 

  102.                     <p>
    103. 

  103.                         Predicates of if and while statements
    104. 

  104.                     </p>
    105. 

  105. 

  106.                     <pre><code contenteditable class="PHP">
    107. 

  107. if ( $foo === 'bar' && ( $user->isAllowed( '' ) || $baz )
    108. 

  108.     && $this->bah() ) {
    109. 

  109.     $this->sendWelcomeMessage();
    110. 

  110. }
    111. 

  111.                     </code></pre>
    112. 

  112. 

  113.                     <pre class="fragment"><code contenteditable class="PHP">
    114. 

  114. if ( $this->isFirstPost() ) {
    115. 

  115.     $this->sendWelcomeMessage();
    116. 

  116. }
    117. 

  117.                     </code></pre>
    118. 

  118.                 </section>
    119. 

  119. 

  120.                 <section>
    121. 

  121.                     <p>
    122. 

  122.                         Bodies of control structures
    123. 

  123.                     </p>
    124. 

  124. 

  125.                     <pre><code contenteditable class="PHP">
    126. 

  126. if ( $this->isFirstPost() ) {
    127. 

  127.     $this->sendWelcomeMessage();
    128. 

  128. }
    129. 

  129.                     </code></pre>
    130. 

  130. 

  131.                     <pre><code contenteditable class="PHP">
    132. 

  132. foreach ( $this->getReviewers() as $reviewer ) {
    133. 

  133.     $this->notifyReviewer( $reviewer );
    134. 

  134. }
    135. 

  135.                     </code></pre>
    136. 

  136.                 </section>
    137. 

  137. 

  138.                 <section>
    139. 

  139.                     <p>
    140. 

  140.                         How much indenting / nesting?
    141. 

  141.                     </p>
    142. 

  142.                 </section>
    143. 

  143. 

  144.                 <section>
    145. 

  145.                     <p>
    146. 

  146.                         Name length rule
    147. 

  147.                     </p>
    148. 

  148. 

  149.                     <pre><code contenteditable class="PHP">
    150. 

  150. $user->remove();
    151. 

  151. 

  152. function remove() {
    153. 

  153.     // ...
    154. 

  154.     $this->removePostsFromDatabase();
    155. 

  155.     // ...
    156. 

  156. }
    157. 

  157.                     </code></pre>
    158. 

  158.                 </section>
    159. 

  159. 

  160.                 <section>
    161. 

  161.                     <p>
    162. 

  162.                         Well written prose
    163. 

  163.                     </p>
    164. 

  164.                     <pre><code contenteditable class="PHP">
    165. 

  165. if ( $this->isFirstPost() ) {
    166. 

  166.     $this->sendWelcomeMessage();
    167. 

  167.     $this->notifyReviewers();
    168. 

  168. }
    169. 

  169.                     </code></pre>
    170. 

  170. 

  171.                     <pre class="fragment"><code contenteditable class="PHP">
    172. 

  172. function notifyReviewers() {
    173. 

  173.     foreach ( $this->reviewers as $reviewer ) {
    174. 

  174.         $reviewer->notify( $this->post );
    175. 

  175.     }
    176. 

  176. }
    177. 

  177.                     </code></pre>
    178. 

  178.                 </section>
    179. 

  179. 

  180.                 <section>
    181. 

  181.                     <h3>Big functions</h3>
    182. 

  182.                     <ul>
    183. 

  183.                         <li>Have multiple functional areas</li>
    184. 

  184.                         <li class="fragment">Functions define scopes</li>
    185. 

  185.                         <li class="fragment">Have variables used throughout</li>
    186. 

  186.                         <li class="fragment">That is what classes are for</li>
    187. 

  187.                         <li class="fragment">Group of functions that use a common set of variables</li>
    188. 

  188.                     </ul>
    189. 

  189.                 </section>
    190. 

  190. 

  191.                 <section>
    192. 

  192.                     <h3>Panic! Lots of small functions!</h3>
    193. 

  193.                     <ul>
    194. 

  194.                         <li class="fragment">Function call overhead</li>
    195. 

  195.                         <li class="fragment">Long time to write all those functions</li>
    196. 

  196.                     </ul>
    197. 

  197.                 </section>
    198. 

  198. 

  199.                 <section>
    200. 

  200.                     <h3>Silly!</h3>
    201. 

  201.                     <p>
    202. 

  202.                         Well named methods, classes and namespaces act like signposts
    203. 

  203.                     </p>
    204. 

  204.                 </section>
    205. 

  205. 

  206.                 <section>
    207. 

  207.                     <p>
    208. 

  208.                         So what makes small functions unsettling?
    209. 

  209.                     </p>
    210. 

  210.                 </section>
    211. 

  211. 

  212.                 <section>
    213. 

  213.                     <p>
    214. 

  214.                         The landscape metaphor
    215. 

  215.                     </p>
    216. 

  216.                 </section>
    217. 

  217. 

  218.                 <section>
    219. 

  219.                     <p>
    220. 

  220.                         Long functions are familiar.<br />
    221. 

  221.                         Like landscapes, we recognize the landmarks
    222. 

  222.                     </p>
    223. 

  223.                 </section>
    224. 

  224. 

  225.                 <section>
    226. 

  226.                     <h3>New people</h3>
    227. 

  227.                     <ul>
    228. 

  228.                         <li class="fragment">Do not recognize anything</li>
    229. 

  229.                         <li class="fragment">Can only start wandering around aimlessly</li>
    230. 

  230.                     </ul>
    231. 

  231.                 </section>
    232. 

  232. 

  233.                 <section>
    234. 

  234.                     <h3>New people + signposts</h3>
    235. 

  235.                     <ul>
    236. 

  236.                         <li>Establish themselves quickly</li>
    237. 

  237.                         <li>Start being productive fast</li>
    238. 

  238.                     </ul>
    239. 

  239.                 </section>
    240. 

  240. 

  241.                 <section>
    242. 

  242.                     <h3>The bedroom metaphor</h3>
    243. 

  243.                     <ul>
    244. 

  244.                         <li class="fragment">Everything lying around at some place well known to you</li>
    245. 

  245.                         <li class="fragment">Mom gets upset and forces you to clean room</li>
    246. 

  246.                         <li class="fragment">You rebel and put things back</li>
    247. 

  247.                         <li class="fragment">Part of growing up is realizing this does not work in teams</li>
    248. 

  248.                     </ul>
    249. 

  249.                 </section>
    250. 

  250. 

  251.                 <section>
    252. 

  252.                     <h3>Call time overhead</h3>
    253. 

  253.                     <ul>
    254. 

  254.                         <li class="fragment">Nanosecond</li>
    255. 

  255.                         <li class="fragment">Compilers are good at optimizing</li>
    256. 

  256.                         <li class="fragment">Time better spend on real performance issues</li>
    257. 

  257.                     </ul>
    258. 

  258.                 </section>
    259. 

  259. 

  260.                 <section>
    261. 

  261.                     <blockquote>
    262. 

  262.                         I'm sorry I had to write you such a long letter,<br />
    263. 

  263.                         but I did not have time to write you a short one
    264. 

  264.                     </blockquote>
    265. 

  265.                     <p>-- Blaise Pascal</p>
    266. 

  266.                     <br />
    267. 

  267. 

  268.                     <ul>
    269. 

  269.                         <li class="fragment">Takes time and effort</li>
    270. 

  270.                         <li class="fragment">Places burden of breaking down on ALL readers</li>
    271. 

  271.                         <li class="fragment">You are a reader as well</li>
    272. 

  272.                     </ul>
    273. 

  273.                 </section>
    274. 

  274. 

  275.                 <section>
    276. 

  276.                     <h3>Example from gerrit</h3>
    277. 

  277.                     <ul>
    278. 

  278.                         <li><a href="https://gerrit.wikimedia.org/r/#/c/78365/2/lib/resources/jquery.wikibase/jquery.wikibase.entityselector.js">Step 0, wrong direction</a></li>
    279. 

  279.                         <li><a href="https://gerrit.wikimedia.org/r/#/c/78365/3/lib/resources/jquery.wikibase/jquery.wikibase.entityselector.js">Step 1, first split</a></li>
    280. 

  280.                         <li><a href="https://gerrit.wikimedia.org/r/#/c/78365/4/lib/resources/jquery.wikibase/jquery.wikibase.entityselector.js">Step 2, second split</a></li>
    281. 

  281.                     </ul>
    282. 

  282.                 </section>
    283. 

  283. 

  284.                 <section data-state="blackout">
    285. 

  285.                     <h2>Function arguments</h2>
    286. 

  286.                 </section>
    287. 

  287. 

  288.                 <section>
    289. 

  289.                     <h3>How many?</h3>
    290. 

  290.                     <ul>
    291. 

  291.                         <li class="fragment">Ideally none, the fewer the better</li>
    292. 

  292.                         <li class="fragment">Arguments are hard to understand</li>
    293. 

  293.                         <li class="fragment">More then 3 requires very special justification</li>
    294. 

  294.                     </ul>
    295. 

  295.                 </section>
    296. 

  296. 

  297.                 <section>
    298. 

  298.                     <section>
    299. 

  299.                         <h3>Flag arguments</h3>
    300. 

  300.                         <p class="fragment">
    301. 

  301.                             Make functions do multiple things!
    302. 

  302.                         </p>
    303. 

  303. 

  304.                         <pre class="fragment"><code contenteditable class="PHP">
    305. 

  305.                             renderHtml( true );
    306. 

  306.                         </code></pre>
    307. 

  307.                     </section>
    308. 

  308. 

  309.                     <section>
    310. 

  310.                        <pre><code contenteditable class="PHP">
    311. 

  311. function renderHtml( $userIsLoggedIn ) {
    312. 

  312.     // ...
    313. 

  313.     if ( $userIsLoggedIn ) {
    314. 

  314.         // ...
    315. 

  315.     }
    316. 

  316.     // ...
    317. 

  317. }
    318. 

  318.                        </code></pre>
    319. 

  319. 

  320.                         <pre class="fragment"><code contenteditable class="PHP">
    321. 

  321. function renderHtmlForLoggedInUser() {
    322. 

  322. 

  323. }
    324. 

  324. 

  325. function renderHtmlForAnonUser() {
    326. 

  326. 

  327. }
    328. 

  328.                         </code></pre>
    329. 

  329. 

  330.                         <pre class="fragment"><code contenteditable class="PHP">
    331. 

  331. renderHtmlForLoggedInUser();
    332. 

  332.                         </code></pre>
    333. 

  333.                     </section>
    334. 

  334.                 </section>
    335. 

  335. 

  336. 

  337.                 <section>
    338. 

  338.                     <h3>Argument objects</h3>
    339. 

  339.                     <pre><code contenteditable class="PHP">
    340. 

  340. function drawCircle( $x, $y, $radius ) {}
    341. 

  341.                     </code></pre>
    342. 

  342. 

  343.                     <pre><code contenteditable class="PHP">
    344. 

  344. function drawCircle( Point $center, $radius ) {}
    345. 

  345.                     </code></pre>
    346. 

  346.                 </section>
    347. 

  347. 

  348.                 <section>
    349. 

  349.                     <h3>Output arguments</h3>
    350. 

  350.                     <pre><code contenteditable class="PHP">
    351. 

  351. appendFooter( $report );
    352. 

  352.                     </code></pre>
    353. 

  353. 

  354.                     <pre><code contenteditable class="PHP">
    355. 

  355. $report->appendFooter();
    356. 

  356.                     </code></pre>
    357. 

  357.                 </section>
    358. 

  358. 

  359.                 <section data-state="blackout">
    360. 

  360.                     <h2>Side effects</h2>
    361. 

  361.                 </section>
    362. 

  362. 

  363.                 <section>
    364. 

  364.                     <p>Either do something OR answer something, not both!</p>
    365. 

  365.                 </section>
    366. 

  366. 

  367.                 <section>
    368. 

  368.                    <pre><code contenteditable class="Java">
    369. 

  369. public boolean set( String attributeName, String value );
    370. 

  370.                    </code></pre>
    371. 

  371. 

  372.                     <pre class="fragment"><code contenteditable class="Java">
    373. 

  373. if ( set( "username", "NyanCat" ) )
    374. 

  374.                     </code></pre>
    375. 

  375.                 </section>
    376. 

  376. 

  377.                 <section>
    378. 

  378.                     <p>Same for returning error codes. Error handling is one thing.</p>
    379. 

  379.                 </section>
    380. 

  380. 

  381.                 <section data-transition="linear">
    382. 

  382.                     <h3>Conclusion</h3>
    383. 

  383.                     <ul>
    384. 

  384.                         <li>Small!</li>
    385. 

  385.                         <li class="fragment">Small well named functions act like signposts</li>
    386. 

  386.                         <li class="fragment">Classes hide in big functions</li>
    387. 

  387.                         <li class="fragment">Functions do one thing, extract till you drop</li>
    388. 

  388.                         <li class="fragment">Minimize arguments</li>
    389. 

  389.                         <li class="fragment">Command query separation</li>
    390. 

  390.                     </ul>
    391. 

  391.                 </section>
    392. 

  392. 

  393.                 <section data-state="blackout" data-transition="linear">
    394. 

  394.                     <h3>These slides</h3>
    395. 

  395.                     <p>CC BY-SA 3.0, <a href="https://twitter.com/#!/JeroenDeDauw">Jeroen De Dauw</a></p>
    396. 

  396.                     <p>
    397. 

  397.                         <a href="https://github.com/JeroenDeDauw/slides/">Clone from GitHub</a>
    398. 

  398.                         or view at <a href="http://bit.ly/clean-functions">bit.ly/clean-functions</a>
    399. 

  399.                     </p>
    400. 

  400. 

  401.                     <div class="fragment">
    402. 

  402.                         <br />
    403. 

  403.                         <h3>Attribution</h3>
    404. 

  404.                         <p>Slide engine: <a href="http://lab.hakim.se/reveal-js/">reveal.js</a>, Copyright (C) 2014 Hakim El Hattab</p>
    405. 

  405.                         <small>
    406. 

  406.                             <br />
    407. 

  407.                             A lot of the material in these slides is based on works by Robert C. Martin.<br />
    408. 

  408.                             In particular his book
    409. 

  409.                             <a href="http://www.goodreads.com/book/show/3735293-clean-code">Clean Code</a>
    410. 

  410.                             , and
    411. 

  411.                             <a href="http://www.cleancoders.com/">Clean Coders</a>
    412. 

  412.                             video series.
    413. 

  413.                         </small>
    414. 

  414.                     </div>
    415. 

  415.                 </section>
    416. 

  416. 

  417.                 <section data-state="blackout" data-transition="linear">
    418. 

  418.                     <h3>Instead of me</h3>
    419. 

  419. 

  420.                     <img height="290px" src="img/clean-code.jpg" />
    421. 

  421.                     <img height="290px" src="img/clean-coder.jpg" />
    422. 

  422.                     <img height="290px" src="img/fowler-enterprise.jpg" />
    423. 

  423.                     <img height="290px" src="img/legacy-code.jpg" />
    424. 

  424.                 </section>
    425. 

  425. 

  426.                 <section data-state="blackout">
    427. 

  427.                     <img src="img/i-has-question-lolcat.jpg" />
    428. 

  428.                 </section>
    429. 

  429. 

  430. 			</div>
    431. 

  431. 

  432. 		</div>
    433. 

  433. 

  434. 		<script src="lib/js/head.min.js"></script>
    435. 

  435. 		<script src="js/reveal.min.js"></script>
    436. 

  436. 

  437. 		<script>
    438. 

  438. 

  439. 			// Full list of configuration options available here:
    440. 

  440. 			// https://github.com/hakimel/reveal.js#configuration
    441. 

  441. 			Reveal.initialize({
    442. 

  442. 				controls: true,
    443. 

  443. 				progress: true,
    444. 

  444. 				history: true,
    445. 

  445. 				center: true,
    446. 

  446. 

  447. 				theme: Reveal.getQueryHash().theme, // available themes are in /css/theme
    448. 

  448. 				transition: Reveal.getQueryHash().transition || 'default', // default/cube/page/concave/zoom/linear/fade/none
    449. 

  449. 

  450. 				// Optional libraries used to extend on reveal.js
    451. 

  451. 				dependencies: [
    452. 

  452. 					{ src: 'lib/js/classList.js', condition: function() { return !document.body.classList; } },
    453. 

  453. 					{ src: 'plugin/markdown/marked.js', condition: function() { return !!document.querySelector( '[data-markdown]' ); } },
    454. 

  454. 					{ src: 'plugin/markdown/markdown.js', condition: function() { return !!document.querySelector( '[data-markdown]' ); } },
    455. 

  455. 					{ src: 'plugin/highlight/highlight.js', async: true, callback: function() { hljs.initHighlightingOnLoad(); } },
    456. 

  456. 					{ src: 'plugin/zoom-js/zoom.js', async: true, condition: function() { return !!document.body.classList; } },
    457. 

  457. 					{ src: 'plugin/notes/notes.js', async: true, condition: function() { return !!document.body.classList; } }
    458. 

  458. 					// { src: 'plugin/leap/leap.js', async: true }
    459. 

  459. 					// { src: 'plugin/search/search.js', async: true, condition: function() { return !!document.body.classList; } }
    460. 

  460. 					// { src: 'plugin/remotes/remotes.js', async: true, condition: function() { return !!document.body.classList; } }
    461. 

  461. 				]
    462. 

  462. 			});
    463. 

  463. 

  464. 		</script>
    465. 

  465. 

  466. 	</body>
    467. 

  467. </html>
    468. 

  468.