Use of VAR type in X++ in new Dynamics AX RTW

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Hi all

I'm sure some of you have seen a new VAR type being used in X++. By declaring an object as VAR, the compiler will calculate the type of declared entity.

Also read about it : https://community.dynamics.com/ax/b/newdynamicsax/archive/2016/02/26/using-var-in-x

Other than this, is the VAR type a really good way to program ? Can this be used to good use in all levels of code or in other objects? What are the real benefits ?

Let's discuss and learn together!!!

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André Arnaud de Cal... 300,917 Super User 2025 Season 2 on at

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Hi Manish,

This is a great question. I think persons with .NET (C#) experience can provide their insights better. Note that there is another blog related to the VAR keyword: blogs.msdn.com/.../x-in-ax7-1-the-var-keyword.aspx

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Martin Dráb 237,807 Most Valuable Professional on at

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Usually it's just a shortcut, so you don't have to declare the type, if it would make code less readable. For example, often the type is obvious or not important and specifying it would make code less readable.

You're welcome to use var where it makes sense, but make sure that you don't make your code less readable by omitting important type information. That the type is obvious to the compiler doesn't meat it's obvious to developers.

In C#, it's also necessary for variables of anonymous types, because there is no way how to declare such a type. For example, you have a LINQ query returning two fields and the framework returns an object with these two fields, but it doesn't have any named type.

Anonymous types are going to be supported in X++ in future.

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Martin Dráb 237,807 Most Valuable Professional on at

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It's probably important to reiterate that var doesn't represent a dynamic type. It's still a static type and compile-time type control is still in place.

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Community Member on at

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Hi Andre,

Is there any restrictions or issues if we use VAR type for a field type in a table. also, is there any conversion functions available to convert VAR to other types?

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Martin Dráb 237,807 Most Valuable Professional on at

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You can use it for local variables; nowhere else.

The type of table fields must be defined at design time, not inferred from how the field it used.

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Martin Dráb 237,807 Most Valuable Professional on at

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The question about conversion shows that you missed the point. VAR is not a type. It's a keyword that allows you not to manually write the type of a variable in code, because the compiler already knows it. For example, var x = "abc" it's exactly the same as str x = "abc". The CIL will be identical.

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Iulian Cordobin 8,201 on at

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As with any other enhancements that will be brought in the X++ compiler from the C# world, this can also be consider a great addition to the options a true developer will have from the programming language. The only thing I would like to add, since Martin already outlined the technical aspects, (as I also noticed as a discussion thread on a C# blog) would be the idea that the power of the var keyword would lie in the ability of each developer to really know when to use it and when to refrain from it.

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Iulian Cordobin 8,201 on at

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To comment further on the idea that the developer should truly understand when to use it or not, is that, as the definition of the VAR keyword becomes more and more obvious, it will be used by some of the lazy developers to really declare their variables as VAR rather than using the type.

This is really where the problem lies: the VAR should be used when the type of the object we get is unknown, but some will abuse its power and start to write less readable code (we know that's true, and hope we will not get to a point where every declaration will be VAR xyz).

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