Sunday, 31 January 2016

X++ in AX7: Readonly keyword

In AX7 X++ now supports the readonly keyword. Semantically it is identical to readonly in C#.

In short; it allows you to define members on a class that can only be initialized in the declaration and in the constructor.

class MyClass
    readonly str identifier = "XYZ";
    readonly str identifier2;

    public void new(str _identifier)
        identifier2 = _identifier;

    public void foo()
        // The field 'identifier2' is read only. A value cannot be assigned to it.
        //identifier2 = "ABC"; 

The big question is "when to use it?" In my opinion the actual use scenarios are limited – simply because other language constructs are still missing.

In X++ we still recommend the construct pattern and the newFrom pattern. These patterns recommend the new method to not have any parameters – readonly has little applicability, when the new method is parameter-less.

So why do we prefer parameter-less new methods?
  1. It enables serialization of classes using the pack/unpack pattern – all classes extending RunBase are subject to this.
  2. It enables the extension framework and smart customizations.
Once X++ supports getters/setters and method overloading (at least of the new method) – then readonly will become handy.'

If you have a good use scenario for readonly - please share in the comments section below.

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