mfp's two cents

...on Dynamics AX Development!
  • mfp's two cents

    Debug::Assert in X++

    • 3 Comments

    Update 4th of August 2014: Clarification of the AX runtime behavior when non-developers hit an assert statement.



      defect free software

    “In computer programming, an assertion is a predicate (a true–false statement) placed in a program to indicate that the developer thinks that the predicate is always true at that place.”    

    http://en.wikipedia.org/wiki/Assertion_(computing)

    What would you rather have: A piece of source code with or without assertions? I’d definitely prefer source code with assertions – it makes the code easier to read, debug and troubleshoot.

    My recommendation is to use assertions in X++ when all of the following are true:

    1. The condition can never be false if the code is correct, and
    2. The condition is not so trivial it obviously be always true, and
    3. The condition is in some sense internal to the component, and
    4. The condition can be verified without any method calls.

     

    1. The condition can never be false if the code is correct

    Assertions and error handling are two different things.

    • Assertions should be used to document logically impossible situations in a correctly implemented program. If the impossible occur, then something is wrong – a programming error has been discovered.
    • Error handling – as the name implies – is the implementation of what should happen when an error occurs. Error handling are valid code paths that determines how the software reacts to various erroneous conditions, like incorrect data entered by the user, to system error conditions like out-of-memory.


    In a nutshell, it should be possible to write unit test for error handling – but not for assertions.

    2. The condition is not so trivial it obviously be always true

    Assert statements takes time to write and read – and if the condition they are asserting is obviously always true, then the assertion is pure clutter – and we are better off without it.

    3. The condition is in some sense internal to the component

    A failing assertion is an indication of a problem with the implementation. Something within the component – regardless of input from the outside world – is broken and needs fixing. Typically, I’d use assertions for input validation in private methods, and exceptions in public methods. Conversely, you don’t want consumers of your component to be hit by assertions – regardless of how they use your component.

    4. The condition can be verified without any method calls.

    Assert statements in X++ are a little special, as the X++ compiler always includes assert statements. In other languages (like C#) you can have multiple compiler targets – and typically the release build would not include the assert statements. In AX when a non-developer is hitting an assert statement, then the runtime will suppress eventual errors. I.e. in a production system assert statements have no functional impact.

    Given assert statements in X++ are always evaluated, and thus degrades performance, they should be used with a bit of caution. If the condition can be verified with minimal overhead – for example that a variable has a certain value – then there is no problem. However; if the assertion requires execution of complex logic, RPC or SQL calls then it should be avoided, due to the performance impact. In cases where the performance impact is significant, but you don’t want to compromise on assertions, the assertions can be wrapped inside a call to Debug::debugMode().

    “without any method calls” is just a guiding principles. Sometimes it makes sense to factor the condition into a Boolean method – for reuse or for clarity – here I would not object.

    Examples

    Here is an example of good use of assertion in X++:

    private void markDetailRecordAsEdited(
    RecId _journalControlDetailId,
    RecId _draftConstraintTreeId) { Debug::assert(_journalControlDetailId != 0); Debug::assert(_draftConstraintTreeId != 0); if (! modifiedDetailRecords.exists(_journalControlDetailId)) { modifiedDetailRecords.insert(
    _journalControlDetailId,
    _draftConstraintTreeId); } }

     

    Here is another example where Debug::debugMode() is used:

    private void render()
    {
        ...
        
        if (Debug::debugMode())
        {
            Debug::assert(this.hierarchyCount() > 0);
            Debug::assert(segments != null);
            Debug::assert(totalSegmentCount > 0);
        }
    
        ...
    }

    Closing remarks

    I once saw a t-shirt with this print on the front: “If debugging is the process of removing bugs, then programming must be the process of putting them in”.  I wish the back had read: “Programming with assertions is one way to keep bugs out.”

  • mfp's two cents

    Microsoft Dynamics ERP software now available on the Azure cloud

    • 0 Comments

    Cloud

    Read more here.

  • mfp's two cents

    SysExtension Framework – to the rescue

    • 5 Comments

    There is a coding pattern that has been proliferating the X++ code base for years. It is not an X++ best practices – nor is it object oriented; yet it is used quite heavily (unfortunately). Consider a simple class hierarchy with an abstract base class and 3 derived classes. A typical implementation of a factory would be a static method on the base class, like this: (Please ignore the type of the parameter – it could  be anything, I choose str for simplicity)

    image

    Now; the problems with this approach are many.

    • First of all the base class has references to the sub classes. Why is that a problem? Consider the base class is a framework class – is it a good idea for framework classes to have references to consumer classes of the framework? Of course not – we don’t like that coupling.
    • Secondarily; the 3 subclasses are all referenced by the same method. Any new sub class would require an update to the factory. This turns the method into a congestion point, and it creates a coupling between sub-classes.

    The coupling between the 4 classes spells trouble. If you try to modularize an application written like this, you will quickly realize that the pattern above is bad. You cannot have references from lower-level models (aka. assemblies/modules) to higher-level models. Yet; having a single factory method is valuable and a good practice.

    SysExtension Framework to the rescue.

    Consider you decorate the subclasses with an attribute, like depicted here:

    image

    Then you can rewrite the factory method to this:

    image

    The extension framework returns an instance of the right subclass automatically. It uses the attribute to determine which subclass instance to create. Quite simple – extraordinary powerful!

    Now notice:

    • Truly decoupled! New subclasses can be added without any changes to the base class.
    • Less code is required! In the example here the delta is not significant – but sometimes you have switch statements spanning hundreds of lines.
    • No change in the public API! The contract stays the same – this is an easy and low risk refactoring.

    A few words of caution: There is a small performance impact on cold systems when using the SysExtension framework. In most cases you will not notice it; however – for performance critical paths, you should measure the impact of this change before going for it.

    To learn more about the SysExtension framework see here.

  • mfp's two cents

    An amazing AX day in Moscow

    • 0 Comments

    Navicon’s AX Fair in Moscow was a big success. Around 150 peopled gather to learn about Microsoft Dynamics AX 2012. There were a few keynotes followed by two breakout tracks, hands-on labs to allow everyone to interact with AX 2012. Also every attendee got a free copy of the Russian version of Inside Dynamics AX 2012. The book has been translated by Navicon – the host of the conference.

    The Fair was dressed in traditional Russian style and colors, including a guy playing the mandolin (I think) most of the day.
    WP_20130607_022
    WP_20130607_003 The first keynote was by Алёна Геклер from Microsoft Russia – I ‘m sorry to say that I missed some of the details, as both the slide deck and the talk was in Russian.

    I followed next, speaking about developing large scale software, and how a MS-Press book is written.

    The next keynote was by Vadim Korepin – who among other things gave Navicon’s expectations to future AX versions.

    Vadim is also my host for the conference, and he has been the main translator of the Russian version of Inside Dynamics AX 2012. He has done a great job, and I’m sure he will be tired tonight.

    WP_20130607_010
    WP_20130607_011 The final keynote was by Oleg Ognev, Director of IT at IZOVOL. He spoke about Izovol’s AX implementation. Izovol is the first live Russian customer running Microsoft Dynamics AX 2012. The talk also covered why AX was chosen over SAP and Oracle - again the talk was in Russian – but my interpretation was that AX is simply much better.

    During lunch there was a book signing session. The excitement around the book truly amazed me – I stopped counting how many hands I’ve shaken and how many dedications I’ve written.

    Being a bit challenged by the language, I selected to attend the few English sessions. I saw Keith Thaulow, EMEA Sales Director, Demand Solutions speaking about the importance of good Forecasts for Sales and Production. The forecasting solution from Demand Solutions can free up cash tied up in Inventory – you can expect to reduce the inventory levels by at least 10%; and whats equally amazing is that the vast majority of companies installing Demand Solutions’ AX Forecasting solution is able to have it fully implemented within the first 6 months. WP_20130607_017
      

    Tonight I’m having a tradition Russian/Ukrainian dinner with developers from the Russian community.

    Спасибо Москва

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June, 2013

mfp's two cents

...on Dynamics AX Development!