--- title: "Adding Method-Missing support to VB.NET using CTru and Typemock Open-AOP" url: "https://osherove.com/blog/2009/2/25/adding-method-missing-support-to-vbnet-using-ctru-and-typemo.md" canonical: "https://osherove.com/blog/2009/2/25/adding-method-missing-support-to-vbnet-using-ctru-and-typemo.html" published: "2009-02-25T17:21:26" updated: "2009-02-25T17:21:26" tags: [".NET", "Agile", "Typemock"] author: "Roy Osherove" description: "I am finding cooler and cooler stuff to achieve using the CThru Engine. A few hours ago I suddenly thought : “CThru intercepts all calls in the system. what happens if they are calls to methods that don’t exist?”…" usage: "Licensed under CC BY 4.0 — reuse, quote and adapt with attribution (Roy Osherove, link to the original page)." license: "https://creativecommons.org/licenses/by/4.0/" --- # Adding Method-Missing support to VB.NET using CTru and Typemock Open-AOP By Roy Osherove February 25, 2009 In [.NET](https://osherove.com/blog/category/net), [Agile](https://osherove.com/blog/category/agile), [Typemock](https://osherove.com/blog/category/typemock) **Historical article** · Originally published February 25, 2009; technical details may be outdated. I am finding cooler and cooler stuff to achieve using the CThru Engine. A few hours ago I suddenly thought : “CThru intercepts all calls in the system. what happens if they are calls to methods that don’t exist?” Logically this led me to: - VB.NET supports late bound invocation (with option strict off – great for COM related stuff) - other languages ([like Ruby](http://rubylearning.com/satishtalim/ruby_method_missing.html)) have a feature called “[MethodMissing](http://rubylearning.com/satishtalim/ruby_method_missing.html)” whereby you get an callback when a missing method is invoked in the system, so you can do whatever you want. - Maybe we can have MethodMissing in VB.NET?? So I set out to achieve this. A couple hours later, I can now do this: ![image](https://osherove.com/img/wb/55cc30f5_weblogs.asp.net_blogs_rosherove_image_thumb_16E5FA38.png) Notice that “NonExistingMethod” really does not exist on the current type (nor does it have any extension methods). I simply register to the **MissingMethodCall** event published by **CThruEngine**, so that I can now control its behavior. And here’s how I handle the event: ![image](https://osherove.com/img/wb/7276cb91_weblogs.asp.net_blogs_rosherove_image_thumb_05259E06.png) If I execute “MyMethod” here’s the output: ![image](https://osherove.com/img/wb/03263b7c_weblogs.asp.net_blogs_rosherove_image_thumb_666B61C2.png) Now, imagine the possibilities.. :) How does it work? Well, in VB.NET, there’s a special class called “Microsoft.VisualBasic.CompilerServices.**NewLateBinding**” that has a method “**LateCall**” that gets called for all late bound method calls. Of course, it also returns a value. I simply (well, not quite) intercept the calls to it and before VB throws an exception, I can let the user of the event return whatever value they want from that method, and then I skip it’s actual call and return the value. This will also work with late bound index calls, property values (set and get) and more. [CThru](http://www.codeplex.com/CThru) is an open source engine that sits on top of the Typemock Open-AOP hooks (part of the new 5.2.2 release). To learn more about CThru and get the tests and source code, [go here](http://www.codeplex.com/CThru). **Update:** I’ve updated the implementation so that it is more like Ruby. If the class being called declares a method named “missing\_method” that takes a MissingMethodArgs parameter, that method will be invoked automatically by the CThru engine, without needing to register to an event: ![image](https://osherove.com/img/wb/b69311a5_weblogs.asp.net_blogs_rosherove_image_thumb_671DDE1F.png) It’s also useful to consider that you can implement “missing\_method” in C# based assemblies. As the C# types are called in a late bound manner from VB, it should work exactly the same. Given: ![image](https://osherove.com/img/wb/ad0148f2_weblogs.asp.net_blogs_rosherove_image_thumb_1EDFFC76.png) We can write this in VB: ![image](https://osherove.com/img/wb/f6d56444_weblogs.asp.net_blogs_rosherove_image_thumb_707650FB.png) ## More in .NET [All posts in .NET](https://osherove.com/blog/category/net) - Mar 16, 2009 ### [Code Formatter plugin for live writer - updated](https://osherove.com/blog/2009/3/16/code-formatter-plugin-for-live-writer-updated.html) - Mar 1, 2009 ### [Method\_Missing: Cool Uses](https://osherove.com/blog/2009/3/1/method_missing-cool-uses.html) - Dec 31, 2008 ### [The morning brew](https://osherove.com/blog/2008/12/31/the-morning-brew.html) - Dec 3, 2008 ### [Isolation frameworks – lessons from the wild](https://osherove.com/blog/2008/12/3/isolation-frameworks-lessons-from-the-wild.html) --- ## About the author **Roy Osherove**: Senior Solutions Architect at AWS working on AI for production and AI-driven development; author of The Art of Unit Testing and Elastic Leadership, with about 20 years of consulting and training on unit testing, TDD, team leadership and continuous delivery. ### Sites - [RobotPaper](https://robotpaper.ai/): This blog: AI patterns and anti-patterns, AI and coding agents, and engineering leadership. - [osherove.com](https://osherove.com): Roy's personal site. Author of The Art of Unit Testing and Elastic Leadership; consulting and training on unit testing, TDD, team leadership and continuous delivery, plus about 20 years of blog posts. - [The Art of Unit Testing](https://www.artofunittesting.com): The Art of Unit Testing, 3rd Edition (Manning): readable, maintainable, trustworthy unit tests, plus TDD workshops in C#, JavaScript, Java and Kotlin. - [5whys.com](https://www.5whys.com): Roy's writing on software team leadership: self-organizing teams, surviving chaos, learning mode and the Elastic Leadership model. - [Pipeline Driven](https://pipelinedriven.org): Continuous delivery and DevOps practices: build patterns, pipeline-friendly testing, DevOps metrics and enterprise DevOps. - [Elastic Leadership](https://www.elasticleadership.com): Elastic Leadership, Roy's framework for software team leaders (survival, learning and self-organizing modes). ### Social - X: https://x.com/royosherove - LinkedIn: https://www.linkedin.com/in/osherove/ ### Contact - Contact form: https://forms.gle/jQSx5KoXvrVA1JCK7 ### License Licensed under CC BY 4.0 — reuse, quote and adapt with attribution (Roy Osherove, link to the original page). License: https://creativecommons.org/licenses/by/4.0/