Welcome!

You will be redirected in 30 seconds or close now.

ColdFusion Authors: Yakov Fain, Jeremy Geelan, Maureen O'Gara, Nancy Y. Nee, Tad Anderson

Related Topics: ColdFusion, Adobe Flex

ColdFusion: Article

Inheritance in ColdFusion: Code Reuse for CFCs

When it comes to code, less is more

Multiple Inheritance
So far we have only considered inheriting into a child CFC a single parent CFC via the extends attribute of the <cfcomponent> tag. Can we inherit multiple CFCs by using the extends attribute of the <cfcomponent> tag? The answer is very intentionally no; multiple inheritance has certain complications (a discussion of these is beyond the scope of this article) and so a deliberate decision was made to allow for only single inheritance in CFML. However, there is a new type of limited multiple inheritance that can be used in CFML deployed via New Atlanta's BlueDragon 7.0: interfaces. An interface is a special type of CFC that cannot be directly instantiated and that can only specify, but not implement, methods. An interface cannot contain any other pseudo-constructor code, including statements that create object properties. An unlimited number of CFC interfaces can be inherited in any CFC by using BlueDragon 7.0's new implements attribute of the <cfcomponent> tag. Such inheritance does not gain a child CFC any new functionality since the methods of the interface are not implemented. What is gained by the child CFC is the requirement that it implement all methods specified in the interfaces it implements. In a sense, an interface defines a contract that any CFC implementing the interface must follow. In order to understand why this is useful, we have to understand another important concept: type matching.

Implementing type matching in CFML code is another way to make it more reliable and maintainable. Type matching involves explicitly specifying how the code is intended to be used, which makes the code easier to read, easier to use properly, and easier to maintain. In addition, an explicit specification of how the code is intended to be used makes it more likely that improper use of the code will be identified sooner rather than later, either via the generation of errors in testing or by inspection of the code. For example, when we define a CFML function/method with the <cffunction> tag, we may use the returnType attribute to specify the type of data that is returned by the function/method. In the same way, when we define a CFML function/method argument with the <cfargument> tag, we may use the type attribute to specify the type of the data that must be supplied for that argument. For either of these attributes, if the specified type is not passed, an error is generated. In addition, for either of these attributes, we may specify the name of a CFC and by doing so we are indicating that the data being passed must be an instance of the specified CFC.

What does type matching with CFC types gain us? It gains us the ability to reliably reference the public properties and methods the specified type defines. In other words, if we specify 'type="simple"' in a <cfargument> tag, we can reference the myMethod method inside the function to which that <cfargument> tag applies because that method is defined in simple.cfc.
Here is where inheritance comes in: because a child CFC inherits all of the properties and methods of its parent CFC, the public properties and methods of the parent CFC can be reliably referenced on an instance of the child CFC. That is, if we specify 'type="exsimple" in a <cfargument> tag, we can reference the myMethod method inside the function to which that <cfargument> applies because that method is defined in simple.cfc and exsimple.cfc inherits simple.cfc. As a result of this behavior, an instance of a child CFC matches the type of its parent CFC and, for that matter, the type of any CFC from which that parent CFC inherits, and any CFC from which that CFC inherits, and so on all the way on up the inheritance chain. It is this very fact that type matching honors inheritance that explains the usefulness of an interface: since an interface is a type that can be inherited, when an object matches the type of an interface, that interface's properties and methods can be referenced reliably on that object.

We have standard CFCs that support standard single inheritance and interfaces that allow for a special type of multiple inheritance that is useful for type matching. But what about something that is between a standard CFC and an interface? BlueDragon 7.0 provides that, too, and it's called an abstract CFC. Like a standard CFC, an abstract CFC allows for the implementation of properties and methods, and like a standard CFC, an abstract CFC may only inherit from a single other CFC. However, like a CFC interface, an abstract CFC also allows for the specification of methods that must be implemented by any CFC that inherits from that abstract CFC, and like a CFC interface, an abstract CFC cannot be instantiated directly. An abstract CFC is a CFC that is not a completed CFC implementation; it is a partial CFC implementation designed specifically to be inherited by CFCs that complete that partial implementation.

Conclusion
We have now seen how inheritance allows us to minimize the amount of CFML we have to write when working with CFCs. Any CFC can inherit the full CFML contents of a single other CFC by extending that CFC. With BlueDragon 7.0, we can use abstract CFCs, a special type of CFC that can be extended but not directly instantiated. In addition, we have seen that with BlueDragon 7.0, a CFC can inherit unimplemented methods from an unlimited number of CFC interfaces, which is useful for CFC type matching.

In order not to detract from the focus of this article, certain object-oriented considerations such as overriding, abstraction, encapsulation (including the use of getter and setter methods), and polymorphism intentionally were not covered and certain statements impacted by such considerations intentionally were not fully qualified.

Resources
If you are interested in a fuller introductory treatment of object-oriented development with CFCs than I was able to give in this article, see the following presentation by Matt Woodward:

www.mattwoodward.com/presentations/cfc_101.pdf

If you are interested in more information on using inheritance as well as on aggregation (a concept not discussed in this article), see Hal Helms's newsletter from March 22, 2003:

www.halhelms.com?fuseaction=newsletters.show&issue=032203_Inheritance

Finally, if you are interested in more information on CFC interfaces and abstract CFCs as supported in BlueDragon 7.0 see the BlueDragon 7.0 cfml Enhancement Guide:

www.newatlanta.com/products/bluedragon/self_help/docs/7_0/ BlueDragon_70_CFML_Enhancements_Guide.pdf

More Stories By Josh Adams

Josh Adams is the developer evangelist for New Atlanta's BlueDragon family of CFML application server products. He presents on a regular basis at technical conferences and user groups throughout North America. Josh is also an active CFML developer both in his role at New Atlanta and in other endeavors.

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


@ThingsExpo Stories
SYS-CON Events announced today that Evatronix will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Evatronix SA offers comprehensive solutions in the design and implementation of electronic systems, in CAD / CAM deployment, and also is a designer and manufacturer of advanced 3D scanners for professional applications.
SYS-CON Events announced today that Synametrics Technologies will exhibit at SYS-CON's 22nd International Cloud Expo®, which will take place on June 5-7, 2018, at the Javits Center in New York, NY. Synametrics Technologies is a privately held company based in Plainsboro, New Jersey that has been providing solutions for the developer community since 1997. Based on the success of its initial product offerings such as WinSQL, Xeams, SynaMan and Syncrify, Synametrics continues to create and hone inn...
To get the most out of their data, successful companies are not focusing on queries and data lakes, they are actively integrating analytics into their operations with a data-first application development approach. Real-time adjustments to improve revenues, reduce costs, or mitigate risk rely on applications that minimize latency on a variety of data sources. In his session at @BigDataExpo, Jack Norris, Senior Vice President, Data and Applications at MapR Technologies, reviewed best practices to ...
"Evatronix provides design services to companies that need to integrate the IoT technology in their products but they don't necessarily have the expertise, knowledge and design team to do so," explained Adam Morawiec, VP of Business Development at Evatronix, in this SYS-CON.tv interview at @ThingsExpo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
Digital Transformation (DX) is not a "one-size-fits all" strategy. Each organization needs to develop its own unique, long-term DX plan. It must do so by realizing that we now live in a data-driven age, and that technologies such as Cloud Computing, Big Data, the IoT, Cognitive Computing, and Blockchain are only tools. In her general session at 21st Cloud Expo, Rebecca Wanta explained how the strategy must focus on DX and include a commitment from top management to create great IT jobs, monitor ...
In his Opening Keynote at 21st Cloud Expo, John Considine, General Manager of IBM Cloud Infrastructure, led attendees through the exciting evolution of the cloud. He looked at this major disruption from the perspective of technology, business models, and what this means for enterprises of all sizes. John Considine is General Manager of Cloud Infrastructure Services at IBM. In that role he is responsible for leading IBM’s public cloud infrastructure including strategy, development, and offering m...
Recently, WebRTC has a lot of eyes from market. The use cases of WebRTC are expanding - video chat, online education, online health care etc. Not only for human-to-human communication, but also IoT use cases such as machine to human use cases can be seen recently. One of the typical use-case is remote camera monitoring. With WebRTC, people can have interoperability and flexibility for deploying monitoring service. However, the benefit of WebRTC for IoT is not only its convenience and interopera...
No hype cycles or predictions of a gazillion things here. IoT is here. You get it. You know your business and have great ideas for a business transformation strategy. What comes next? Time to make it happen. In his session at @ThingsExpo, Jay Mason, an Associate Partner of Analytics, IoT & Cybersecurity at M&S Consulting, presented a step-by-step plan to develop your technology implementation strategy. He also discussed the evaluation of communication standards and IoT messaging protocols, data...
Product connectivity goes hand and hand these days with increased use of personal data. New IoT devices are becoming more personalized than ever before. In his session at 22nd Cloud Expo | DXWorld Expo, Nicolas Fierro, CEO of MIMIR Blockchain Solutions, will discuss how in order to protect your data and privacy, IoT applications need to embrace Blockchain technology for a new level of product security never before seen - or needed.
Recently, REAN Cloud built a digital concierge for a North Carolina hospital that had observed that most patient call button questions were repetitive. In addition, the paper-based process used to measure patient health metrics was laborious, not in real-time and sometimes error-prone. In their session at 21st Cloud Expo, Sean Finnerty, Executive Director, Practice Lead, Health Care & Life Science at REAN Cloud, and Dr. S.P.T. Krishnan, Principal Architect at REAN Cloud, discussed how they built...
Nordstrom is transforming the way that they do business and the cloud is the key to enabling speed and hyper personalized customer experiences. In his session at 21st Cloud Expo, Ken Schow, VP of Engineering at Nordstrom, discussed some of the key learnings and common pitfalls of large enterprises moving to the cloud. This includes strategies around choosing a cloud provider(s), architecture, and lessons learned. In addition, he covered some of the best practices for structured team migration an...
The 22nd International Cloud Expo | 1st DXWorld Expo has announced that its Call for Papers is open. Cloud Expo | DXWorld Expo, to be held June 5-7, 2018, at the Javits Center in New York, NY, brings together Cloud Computing, Digital Transformation, Big Data, Internet of Things, DevOps, Machine Learning and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding busin...
"Digital transformation - what we knew about it in the past has been redefined. Automation is going to play such a huge role in that because the culture, the technology, and the business operations are being shifted now," stated Brian Boeggeman, VP of Alliances & Partnerships at Ayehu, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
In his session at 21st Cloud Expo, Raju Shreewastava, founder of Big Data Trunk, provided a fun and simple way to introduce Machine Leaning to anyone and everyone. He solved a machine learning problem and demonstrated an easy way to be able to do machine learning without even coding. Raju Shreewastava is the founder of Big Data Trunk (www.BigDataTrunk.com), a Big Data Training and consulting firm with offices in the United States. He previously led the data warehouse/business intelligence and B...
Cloud Expo | DXWorld Expo have announced the conference tracks for Cloud Expo 2018. Cloud Expo will be held June 5-7, 2018, at the Javits Center in New York City, and November 6-8, 2018, at the Santa Clara Convention Center, Santa Clara, CA. Digital Transformation (DX) is a major focus with the introduction of DX Expo within the program. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive ov...
A strange thing is happening along the way to the Internet of Things, namely far too many devices to work with and manage. It has become clear that we'll need much higher efficiency user experiences that can allow us to more easily and scalably work with the thousands of devices that will soon be in each of our lives. Enter the conversational interface revolution, combining bots we can literally talk with, gesture to, and even direct with our thoughts, with embedded artificial intelligence, whic...
Smart cities have the potential to change our lives at so many levels for citizens: less pollution, reduced parking obstacles, better health, education and more energy savings. Real-time data streaming and the Internet of Things (IoT) possess the power to turn this vision into a reality. However, most organizations today are building their data infrastructure to focus solely on addressing immediate business needs vs. a platform capable of quickly adapting emerging technologies to address future ...
With tough new regulations coming to Europe on data privacy in May 2018, Calligo will explain why in reality the effect is global and transforms how you consider critical data. EU GDPR fundamentally rewrites the rules for cloud, Big Data and IoT. In his session at 21st Cloud Expo, Adam Ryan, Vice President and General Manager EMEA at Calligo, examined the regulations and provided insight on how it affects technology, challenges the established rules and will usher in new levels of diligence arou...
22nd International Cloud Expo, taking place June 5-7, 2018, at the Javits Center in New York City, NY, and co-located with the 1st DXWorld Expo will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud ...
22nd International Cloud Expo, taking place June 5-7, 2018, at the Javits Center in New York City, NY, and co-located with the 1st DXWorld Expo will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud ...