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.