What is difference between using a command $classmethod rather than just invoking them straight away?

Question

Question

Kishan Ravindran · Dec 26, 2017

#Beginner #Object Data Model #ObjectScript #Caché

For example if i need to call a class and its method i can just use like

do ##class(circle).radius()

rather than using

do $classmethod("circle",radius)

(I suppose both of them doing the same function i am not aware of it)

Please help me understand what is different and is there any specific usage.

Correct me if i have made mistake.

Discussion (7)0

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Evgeny Shvarov · Dec 26, 2017

How to call a classmethod?

If you are inside the class Circle call it with:

do ..Radius()

If you call this method from another class use:

do ##class(Circle).Radius()

But there are cases when you do not know either name of a class or name of a method on runtime. So $classmethod is your friend here:

do $classmethod("Circle","Radius")

HTH

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score 2 · Answer 1 · 2017-12-26T06:44:03-05:00

the key difference is that you can pass the classname by a variable.
So you are prepared to get the classname passed by some other method.

In your example with a constant string"circle"you miss the key advantage and It's of o added value.

BTW. Correct is $classmethod("circle.radius","%New")

http://docs.intersystems.com/latest/csp/docbook/DocBook.UI.Page.cls?KEY=...

score 0 · Answer 2 · 2017-12-26T08:36:13-05:00

So can this is be used in a parent-child class format if how will this be of use. And by using $classmethod this is there any advantage, if so can you mention some.

Thanks

Kishan R

score 0 · Answer 3 · 2017-12-26T10:50:11-05:00

Eduard Lebedyuk · Dec 26, 2017

You can call methods of parent class with ##super(arg1)

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score 0 · Answer 4 · 2017-12-26T06:44:59-05:00

The key difference of $classmethod is runtime:

$CLASSMETHOD permits a ObjectScript program to invoke an arbitrary class method in an arbitrary class. Both the class name and the method name may be computed at runtime or supplied as string constants.^proof

score 0 · Answer 5 · 2017-12-26T08:13:48-05:00

Eduard Lebedyuk · Dec 26, 2017

If you can, always invoke code directly:

do ##class(circle).radius()

Use classmethod only if you can't invoke method directly.

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score 0 · Answer 6 · 2017-12-27T13:34:28-05:00

Guilherme Silva · Dec 27, 2017

I think in case you need to call a lot of methods in programatic mode, you can do it this way, btw is easier.

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