What is the Difference Between Methods and Class Methods?
What is the difference between method and class method and why are mentioning one as Method and class method what is the purpose of this?
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Hi Kishan
A method is attached to a specific instance of an Object class. A Classmethod can be called without having to instantiate the object.
So, we could have a Method on a Person object to update address
do person.UpdateAddress("New address")
Whereas, for a ClassMethod, we could define a Classmethod to give us as object instance to then work on
set person = ##class(User.Person).CreatePerson("FirstName","LastName",Age)
Hope that helps?
Thank you Alex can you tell why we using Method and Class Method can't we just use a class method itself ?
Please read doc here:
Also there is a good introductory book in documentation: "Caché Programming Orientation Guide" http://docs.intersystems.com/latest/csp/docbook/DocBook.UI.Page.cls?KEY=GORIENT
Not sure if I understood what you meant, but I'll try to answer:
When using class methods you cannot reference your THIS instance. Have you every used Java, C# or whatever programming language that supports object oriented-programming paradigms? If so then class methods are the same as static methods.
Common (non-static) methods have the advantage of providing you the instance context. Which means that all properties are accessible inside this kind of method, even the private ones.
Class Sample.Person Extends %Persistent
{
Property Name As %String;
ClassMethod GetPersonName(instance As Sample.Person)
{
return instance.Name // This works fine, GetPersonName is receiving an external Sample.Person.
}
// 'My' is used to empathize that this method refers to it's own instance name.
Method GetMyName() As %String
{
return ..Name // This also works fine. Notice that this method doesn't receives the instance, it's because you can only call it from a instance already.
}
ClassMethod GetMyInstanceName() As %String
{
return ...Name // This won't work. Since there's no context (instance). The compiler will even warn about it.
}
}A class method is what other languages usually call a static method. One that can be called even without an instance of that class existing.
Let's imagine you have a class Circle. It may have its own radius in a property
set myCircle = ##class(Circle).%New(25)
write myCircle.radius // 25
write myCircle.getArea() // the calculated area based on its own radius
But now you want to quickly calculate the area of a circle with radius 5, but you don't want to instantiate a new Circle object just for that. So you could have a ClassMethod inside the Circle Class that does that for you
write Circle.calcRadius(5)
You could also smash lots of utility functions as ClassMethods into a Utils class.
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When you have just a Method you need to instantiate the class to run this method.
When you use ClassMethod is a static method so you can call directly it's not necessary to
instantiate
Technically speaking class method is a function from class whereas method is a function from arguments defined inside the class