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.


IoT & Smart Cities Stories
SYS-CON Events announced today that IoT Global Network has been named “Media Sponsor” of SYS-CON's @ThingsExpo, which will take place on June 6–8, 2017, at the Javits Center in New York City, NY. The IoT Global Network is a platform where you can connect with industry experts and network across the IoT community to build the successful IoT business of the future.
CloudEXPO New York 2018, colocated with DXWorldEXPO New York 2018 will be held November 11-13, 2018, in New York City and will bring together Cloud Computing, FinTech and Blockchain, Digital Transformation, Big Data, Internet of Things, DevOps, AI, Machine Learning and WebRTC to one location.
Andrew Keys is Co-Founder of ConsenSys Enterprise. He comes to ConsenSys Enterprise with capital markets, technology and entrepreneurial experience. Previously, he worked for UBS investment bank in equities analysis. Later, he was responsible for the creation and distribution of life settlement products to hedge funds and investment banks. After, he co-founded a revenue cycle management company where he learned about Bitcoin and eventually Ethereal. Andrew's role at ConsenSys Enterprise is a mul...
The best way to leverage your Cloud Expo presence as a sponsor and exhibitor is to plan your news announcements around our events. The press covering Cloud Expo and @ThingsExpo will have access to these releases and will amplify your news announcements. More than two dozen Cloud companies either set deals at our shows or have announced their mergers and acquisitions at Cloud Expo. Product announcements during our show provide your company with the most reach through our targeted audiences.
DXWorldEXPO | CloudEXPO are the world's most influential, independent events where Cloud Computing was coined and where technology buyers and vendors meet to experience and discuss the big picture of Digital Transformation and all of the strategies, tactics, and tools they need to realize their goals. Sponsors of DXWorldEXPO | CloudEXPO benefit from unmatched branding, profile building and lead generation opportunities.
Disruption, Innovation, Artificial Intelligence and Machine Learning, Leadership and Management hear these words all day every day... lofty goals but how do we make it real? Add to that, that simply put, people don't like change. But what if we could implement and utilize these enterprise tools in a fast and "Non-Disruptive" way, enabling us to glean insights about our business, identify and reduce exposure, risk and liability, and secure business continuity?
DXWorldEXPO LLC announced today that Telecom Reseller has been named "Media Sponsor" of CloudEXPO | DXWorldEXPO 2018 New York, which will take place on November 11-13, 2018 in New York City, NY. Telecom Reseller reports on Unified Communications, UCaaS, BPaaS for enterprise and SMBs. They report extensively on both customer premises based solutions such as IP-PBX as well as cloud based and hosted platforms.
Digital Transformation: Preparing Cloud & IoT Security for the Age of Artificial Intelligence. As automation and artificial intelligence (AI) power solution development and delivery, many businesses need to build backend cloud capabilities. Well-poised organizations, marketing smart devices with AI and BlockChain capabilities prepare to refine compliance and regulatory capabilities in 2018. Volumes of health, financial, technical and privacy data, along with tightening compliance requirements by...
In this Women in Technology Power Panel at 15th Cloud Expo, moderated by Anne Plese, Senior Consultant, Cloud Product Marketing at Verizon Enterprise, Esmeralda Swartz, CMO at MetraTech; Evelyn de Souza, Data Privacy and Compliance Strategy Leader at Cisco Systems; Seema Jethani, Director of Product Management at Basho Technologies; Victoria Livschitz, CEO of Qubell Inc.; Anne Hungate, Senior Director of Software Quality at DIRECTV, discussed what path they took to find their spot within the tec...
To Really Work for Enterprises, MultiCloud Adoption Requires Far Better and Inclusive Cloud Monitoring and Cost Management … But How? Overwhelmingly, even as enterprises have adopted cloud computing and are expanding to multi-cloud computing, IT leaders remain concerned about how to monitor, manage and control costs across hybrid and multi-cloud deployments. It’s clear that traditional IT monitoring and management approaches, designed after all for on-premises data centers, are falling short in ...