Home > Articles > Process Improvement

Robert C. Martin's Clean Code Tip of the Week #11: Output Arguments are Counterintuitive

  • Print
  • + Share This
We join "The Craftsman," Robert C. Martin's series on an interstellar spacecraft where programmers hone their coding skills. In this eleventh tip in the series, the crew learns that if your function must change the state of something, have it change the state of the object it is called on.
Like this article? We recommend

Saturday, September 1, 1945, 10:45AM GMT, Caen, France.

Corporal Murphy and Leftenant Haynes crouched behind an overturned horse-cart that had been filled with bricks. The bricks made a reasonable bulwark against the potshots of the sniper in the second floor of the storefront across the street.

“Can you see him, Audie?” Haynes asked?

“Nah, I recon I’ll have to wait for him to shoot at us again. I don’t suppose you’d care to wave your rifle in the air to draw his fire?”

Haynes just glared at his diminutive companion. He was glad that the Americans had sent so many troops to help England fight back the remnants of the German occupation forces, and clean up the mess in Europe, but this particular Texan reminded him a bit too much of the movies about the American west he used to like to watch in the cinema.

The Texan picked up a brick and handed it to Haynes. “When I tell you to, toss that brick over to the right about 30 feet.”

Haynes took the brick and watched as Murphy took aim on the building. Then Murphy said: “Go!” and Haynes tossed the brick. Murphy’s rifle cracked a second after the brick hit the ground.

“That fella got a little too curious. I don’t recon he’ll be curious about anything else again. We’d best get movin’.”

Haynes nodded, and the two of them dashed across the street and into the store. As he ran, Haynes wondered how the battle for London was going.


Thu, 16 Mar 2002, 11:00

“Hey Hotshot, got a minute?”

I was just coming back from a break and happened to walk past Jasmine’s workstation. I happen to walk past Jasmine’s workstation a lot.

“What’s up, Jasmine?”

“Look at this code. What does this mean to you?”

She had highlighted one line on her screen.

 impactCount += scanImpacts(ImpactType.SMALL_PUNCTURE, impacts);

“Oh, you must be working with the micrometeoroid impact locator app. I’ve heard that’s a real mess.”

Jasmine smiled and sneered at the same time.

“Yeah, it was written about ten years ago, and it’s pretty tough to work with.”

I looked more closely at the line of code she had highlighted.

“OK, so it’s counting the number of small punctures in the impacts list.”

“Yeah, that’s what I thought too.”

“You mean that’s not what it does?”

Jasmine fixed me with those gimlet green eyes and shook her head. Her long black hair shimmered and danced.

“No, that’s not at all what it does.”

I snapped back to reality. “Uh… it’s not?”

Jasmine chuckled and said: “Dyson to Alphonse, are you there? No Hotshot, that’s not what this line of code does. – Hay Jerry, got a minute?”

I’d noticed that Jerry happened to walk past Jasmine’s workstation a lot too.

“I swear, Jasmine, whatever it is, I didn’t do it!”

I laughed under my breath. The dressing down she had given him yesterday had been pretty funny.

“Relax, Jerry, I just want you to look at some code.”

“Who wrote it? If it was me, forget it!”

“No, it wasn’t you, Jerry, it was written ten years ago by Jean.”

Jean stood up from her workstation. “Did someone mention my name?”

Jasmine smiled at her and said: “We’re just looking at some code you wrote a long time ago, Jean.”

Jean’s grin and eyes got wide. “Oh my dears, I wish you lots of luck with that. Call me if you need me.” And she sat back down.

Jerry had been looking at the highlighted line of code.

“This is part of that old micrometeoroid impact locator isn’t it?” And then under his breath: “What a dog that system is. Anyway, it looks like this statement scans the impacts list for small punctures.”

“That’s what I thought too.” I blurted. “But Jasmine says no.”

Jerry looked confused. “I don’t see what else it could be doing. It scans the impacts list for impacts that have been classified as ImpactType.SMALL_PUNCTURE.

Jasmine laughed and said: “I love it when you talk to me in code, Jerry.”

Jerry’s mouth tightened.

Jasmine continued. “But, no, that’s not what this line of code does. Not even close.”

I had been looking at the rest of the code on the screen, and I noticed something.

“Jasmine, I think you’re wrong. Look at the line three lines above the one you have highlighted.”

Jasmine smiled evilly, and moved the highlight up.

“You mean this line, Alphonse?”

List<Impact> impacts =
ImpactDB.getImpacts();

“Yeah, it’s reading the impact list from the database. That makes perfect sense if the other line is scanning that list for small punctures.”

Jasmine’s smile got even broader. “Yes, that does make prefect sense. But that’s not what’s going on. Here, look at this.”

Jasmine scrolled up a few more lines.

ImpactDB.setFilter(ImpactType.SMALL_PUNCTURE);

Jerry and I looked at that line for a long time.

“Confusing, isn’t it?” asked Jasmine.

“Yeah.” Said Jerry. “Why are they filtering on small punctures and then scanning for small punctures. That seems redundant.”

I just shook my head.

Jasmine nodded and scrolled down about 20 lines. “Now look at this. Keep in mind that the filter is still set.”

ImpactDB.saveImpacts(impacts);

“Yikes! This is awful!” I blurted. Then I realized that Jean probably heard me. Jerry and Jasmine just snickered.

“Yeah, it’s pretty bad.” Said Jasmine quietly. “So, any guess as to what that original line of code does?”

Jerry pointed at the screen. “I guess it depends on what that filter is doing.”

“Yeah.” Jasmine agreed. “It does.”

“I don’t get it.” I said. “Why would you read something, scan it, and then write it. Nothing in this code changes the impacts list.”

Jasmine looked at me out of the corner of her green eyes. “Are you sure about that Hotshot? Look again at the line I called you over here for.”

My eyes scanned up the screen until I saw it.

 impactCount += scanImpacts(ImpactType.SMALL_PUNCTURE, impacts);

It took about twenty seconds. Then:

“Oh! The impacts list is an output! Oh! The scanImpacts function gets all the impacts from some other source and puts them into the impacts list. Oh!”

Jerry rolled his eyes. “Of course. Duh; impacts is an output.

“Yes, dears. The impacts list is an output.”

Jean had managed to appear right next to us while we were all staring at the screen.

She continued: “We didn’t know any better in those days, my dears. We did the best we could with what we knew, but we didn’t know that much. So we made really terrible errors like this one…and so many others.”

“There was a time, my dears, when we weren’t sure this ship would survive…oh but let’s not talk about that.”

The three of us were stunned. The ship’s survival was never in question. Not ever. What was she talking about?

“Fortunately for us, dears, Mr. C. taught us how to write much better code. You should all go look at rule F2.”

With that, Jean sauntered back to her workstation.

Jasmine smiled at us like the cat with feathers on her mouth. She silently brought up Mr. C’s rules.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020