21
Fri, Jun
3 New Articles

RPG Academy: Parameters: Do You Know Your Options?, Part 2

RPG
Typography
  • Smaller Small Medium Big Bigger
  • Default Helvetica Segoe Georgia Times

The *NOPASS option is very useful, but it's not the perfect solution for every situation. This TechTip continues to discuss the different options available, explaining what *OMIT is and when and how to use it.

 

What if you need the 21st and 22nd parameters of a procedure's parameter list with 40 parameters to be optional? Should you change the procedure's parameters, making the 23rd to 40th parameters optional too? That means validating whether all those parameters were passed and assigning default values to each of them. Not the best of solutions, right? This is the most annoying shortcoming of *NOPASS.

 

Fortunately for you and me (and all the other RPG programmers out there), the great minds behind RPG thought about this and came up with another option, similar to *NOPASS, that doesn't have this problem. The *OMIT option allows you to make a parameter optional, without having to do the same to all the parameters that come after it in the list. As you might expect, it also requires a bit of coding to use safely. Let's continue to use the previous TechTip's example: our USD_to_EUR function will have its functionality extended and will now convert any valid currency to EUR and return a status code as an output parameter. If I'd use *NOPASS, things might get cumbersome as the number of parameters grows, making it harder to code and understand later (yes, because most code is read way more often than it's written/modified). So the new Prototype Definition is as follows:

 

*------------------------------------------------------------------------*

*   Cvt_To_Eur: Converts a currency to Eur at the current exchange rate    

*   This function accepts an Amount (11, 2)

*   An optional date (8, 0)

*   And currency ISO code (3, A) as input parameters.

*   It also includes a status code (4, 0) as output parameter.

*   It returns an EUR Amount (11, 2)

*------------------------------------------------------------------------*

D Cvt_to_Eur     PR           11 2              

* Input parameter: Amount in US Dollars

D P_USD_Amt                   11 2 Value

* Input parameter: exchange rate date (latest available if not specified)

D P_Rate_Date                 8 0 OPTIONS(*OMIT)

* Input parameter: currency ISO code (defaults to USD if not specified)

D P_Curr_Code                 8 0 OPTIONS(*OMIT)

* Output parameter: status code

D P_Status_code               3A

 

As I said before, the Prototype Interface would also need to be changed in a similar manner.

 

Anyway, the first thing to note here is that there are two optional parameters in the middle of the list, which is not possible with *NOPASS. Great! Then why use *NOPASS at all? Well, *OMIT also has a peculiar "feature" that can be a bit annoying: in order to call a function that has parameters with this option, you have to pass all the parameters on every call. If you don't want to specify a parameter, just pass the *OMIT special value in its place. I'm not sure if you remember, but with *NOPASS, you can choose not to pass the optional parameters at all. Let me illustrate this with an example of a typical call of each function:

 

* Calling USD_TO_EUR without the optional parameter

C                   EVAL     W_EUR_Amt = USD_to_EUR(W_USD_Amt)

 

* Calling Cvt_TO_EUR without the optional parameters

C                   EVAL     W_EUR_Amt = Cvt_to_EUR(W_USD_Amt :

C                                                   *Omit :

C                                                   *Omit :

C                                                   W_StsCode)

 

Since you have to pass all the parameters on every call, the %PARMS BIF can't be used to determine if the optional parameter was passed or not. Instead, you have to use the %ADDR BIF to determine if the *OMIT special value was passed. When you pass *OMIT, there's no memory address for your variable because you're not really passing a value; in other words, its memory address is void or *NULL. The code below could be part of the Cvt_to_EUR function:

 

* Check if the date was passed and fill W_Rate_Date accordingly

C                   IF       %ADDR(P_Rate_Date) <> *NULL

C                   EVAL     W_Rate_Date = P_Rate_Date

C                   ELSE

C                   EVAL     W_Rate_Date = *HIVAL

C                   ENDIF

* Check if the Curr. Code was passed and fill W_Curr_Code accordingly

C                   IF       %ADDR(P_Curr_Code) <> *NULL

C                   EVAL     W_Curr_Code = P_Curr_Code

C                   ELSE

C                   EVAL     W_Curr_Code = 'USD'

C                   ENDIF

* Then use the W_Curr_Code to look for the appropriate rate

 

As you can see, it's similar to the *NOPASS/%PARM combination. The %ADDR is used to determine if the *OMIT special value was used and, just like before, the work variable is set accordinglyin this case, using a default value.

 

Finally, a few notes of caution about these two options:

  • Be sure to check every single parameter that uses *NOPASS or *OMIT with the appropriate BIF.
  • Always define a work variable similar to the parameter that you need to test with a name that somehow links the parameter and work variable together. For instance, use the same name with different prefixes: P_ for the parameter and W_ for the work variable.
  • Decide what to do when the parameter is not passed or omitted before you start to write the code. This can be assigning a default value to the work variable, executing a different piece of code, or some other task, in order to keep the procedure or function working properly.

 

If you really want to complicate things, you can use both options in the same parameter:

 

(…)

D P_Some_Parm                 8 0 OPTIONS(*NOPASS : *OMIT)

(…)

 

I never actually had to use this, but I'm sure that there are situations in which it might be useful.

 

Just like the VALUE vs. CONST discussion, there's no right or wrong solution when it comes to the *NOPASS vs. *OMIT debate. It's up to you to decide when to use each, carefully considering the pros and cons of each approach and choosing the best for the case at hand.

 

The next TechTip will be about the remaining options. As usual, feel free to share your thoughts on this in the comments!

 

Rafael Victoria-Pereira

Rafael Victória-Pereira has more than 20 years of IBM i experience as a programmer, analyst, and manager. Over that period, he has been an active voice in the IBM i community, encouraging and helping programmers transition to ILE and free-format RPG. Rafael has written more than 100 technical articles about topics ranging from interfaces (the topic for his first book, Flexible Input, Dazzling Output with IBM i) to modern RPG and SQL in his popular RPG Academy and SQL 101 series on mcpressonline.com and in his books Evolve Your RPG Coding and SQL for IBM i: A Database Modernization Guide. Rafael writes in an easy-to-read, practical style that is highly popular with his audience of IBM technology professionals.

Rafael is the Deputy IT Director - Infrastructures and Services at the Luis Simões Group in Portugal. His areas of expertise include programming in the IBM i native languages (RPG, CL, and DB2 SQL) and in "modern" programming languages, such as Java, C#, and Python, as well as project management and consultancy.


MC Press books written by Rafael Victória-Pereira available now on the MC Press Bookstore.

Evolve Your RPG Coding: Move from OPM to ILE...and Beyond Evolve Your RPG Coding: Move from OPM to ILE...and Beyond
Transition to modern RPG programming with this step-by-step guide through ILE and free-format RPG, SQL, and modernization techniques.
List Price $79.95

Now On Sale

Flexible Input, Dazzling Output with IBM i Flexible Input, Dazzling Output with IBM i
Uncover easier, more flexible ways to get data into your system, plus some methods for exporting and presenting the vital business data it contains.
List Price $79.95

Now On Sale

SQL for IBM i: A Database Modernization Guide SQL for IBM i: A Database Modernization Guide
Learn how to use SQL’s capabilities to modernize and enhance your IBM i database.
List Price $79.95

Now On Sale

BLOG COMMENTS POWERED BY DISQUS

LATEST COMMENTS

Support MC Press Online

$0.00 Raised:
$

Book Reviews

Resource Center

  • SB Profound WC 5536 Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application. You can find Part 1 here. In Part 2 of our free Node.js Webinar Series, Brian May teaches you the different tooling options available for writing code, debugging, and using Git for version control. Brian will briefly discuss the different tools available, and demonstrate his preferred setup for Node development on IBM i or any platform. Attend this webinar to learn:

  • SB Profound WP 5539More than ever, there is a demand for IT to deliver innovation. Your IBM i has been an essential part of your business operations for years. However, your organization may struggle to maintain the current system and implement new projects. The thousands of customers we've worked with and surveyed state that expectations regarding the digital footprint and vision of the company are not aligned with the current IT environment.

  • SB HelpSystems ROBOT Generic IBM announced the E1080 servers using the latest Power10 processor in September 2021. The most powerful processor from IBM to date, Power10 is designed to handle the demands of doing business in today’s high-tech atmosphere, including running cloud applications, supporting big data, and managing AI workloads. But what does Power10 mean for your data center? In this recorded webinar, IBMers Dan Sundt and Dylan Boday join IBM Power Champion Tom Huntington for a discussion on why Power10 technology is the right strategic investment if you run IBM i, AIX, or Linux. In this action-packed hour, Tom will share trends from the IBM i and AIX user communities while Dan and Dylan dive into the tech specs for key hardware, including:

  • Magic MarkTRY the one package that solves all your document design and printing challenges on all your platforms. Produce bar code labels, electronic forms, ad hoc reports, and RFID tags – without programming! MarkMagic is the only document design and print solution that combines report writing, WYSIWYG label and forms design, and conditional printing in one integrated product. Make sure your data survives when catastrophe hits. Request your trial now!  Request Now.

  • SB HelpSystems ROBOT GenericForms of ransomware has been around for over 30 years, and with more and more organizations suffering attacks each year, it continues to endure. What has made ransomware such a durable threat and what is the best way to combat it? In order to prevent ransomware, organizations must first understand how it works.

  • SB HelpSystems ROBOT GenericIT security is a top priority for businesses around the world, but most IBM i pros don’t know where to begin—and most cybersecurity experts don’t know IBM i. In this session, Robin Tatam explores the business impact of lax IBM i security, the top vulnerabilities putting IBM i at risk, and the steps you can take to protect your organization. If you’re looking to avoid unexpected downtime or corrupted data, you don’t want to miss this session.

  • SB HelpSystems ROBOT GenericCan you trust all of your users all of the time? A typical end user receives 16 malicious emails each month, but only 17 percent of these phishing campaigns are reported to IT. Once an attack is underway, most organizations won’t discover the breach until six months later. A staggering amount of damage can occur in that time. Despite these risks, 93 percent of organizations are leaving their IBM i systems vulnerable to cybercrime. In this on-demand webinar, IBM i security experts Robin Tatam and Sandi Moore will reveal:

  • FORTRA Disaster protection is vital to every business. Yet, it often consists of patched together procedures that are prone to error. From automatic backups to data encryption to media management, Robot automates the routine (yet often complex) tasks of iSeries backup and recovery, saving you time and money and making the process safer and more reliable. Automate your backups with the Robot Backup and Recovery Solution. Key features include:

  • FORTRAManaging messages on your IBM i can be more than a full-time job if you have to do it manually. Messages need a response and resources must be monitored—often over multiple systems and across platforms. How can you be sure you won’t miss important system events? Automate your message center with the Robot Message Management Solution. Key features include:

  • FORTRAThe thought of printing, distributing, and storing iSeries reports manually may reduce you to tears. Paper and labor costs associated with report generation can spiral out of control. Mountains of paper threaten to swamp your files. Robot automates report bursting, distribution, bundling, and archiving, and offers secure, selective online report viewing. Manage your reports with the Robot Report Management Solution. Key features include:

  • FORTRAFor over 30 years, Robot has been a leader in systems management for IBM i. With batch job creation and scheduling at its core, the Robot Job Scheduling Solution reduces the opportunity for human error and helps you maintain service levels, automating even the biggest, most complex runbooks. Manage your job schedule with the Robot Job Scheduling Solution. Key features include:

  • LANSA Business users want new applications now. Market and regulatory pressures require faster application updates and delivery into production. Your IBM i developers may be approaching retirement, and you see no sure way to fill their positions with experienced developers. In addition, you may be caught between maintaining your existing applications and the uncertainty of moving to something new.

  • LANSAWhen it comes to creating your business applications, there are hundreds of coding platforms and programming languages to choose from. These options range from very complex traditional programming languages to Low-Code platforms where sometimes no traditional coding experience is needed. Download our whitepaper, The Power of Writing Code in a Low-Code Solution, and:

  • LANSASupply Chain is becoming increasingly complex and unpredictable. From raw materials for manufacturing to food supply chains, the journey from source to production to delivery to consumers is marred with inefficiencies, manual processes, shortages, recalls, counterfeits, and scandals. In this webinar, we discuss how:

  • The MC Resource Centers bring you the widest selection of white papers, trial software, and on-demand webcasts for you to choose from. >> Review the list of White Papers, Trial Software or On-Demand Webcast at the MC Press Resource Center. >> Add the items to yru Cart and complet he checkout process and submit

  • Profound Logic Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application.

  • SB Profound WC 5536Join us for this hour-long webcast that will explore:

  • Fortra IT managers hoping to find new IBM i talent are discovering that the pool of experienced RPG programmers and operators or administrators with intimate knowledge of the operating system and the applications that run on it is small. This begs the question: How will you manage the platform that supports such a big part of your business? This guide offers strategies and software suggestions to help you plan IT staffing and resources and smooth the transition after your AS/400 talent retires. Read on to learn: