method vs function

Monkey Forums/Monkey Beginners/method vs function

dubbsta

(Posted 2014) [#1]

what is the purpose of a method if its just like a function and what does "self" do
pls help.

therevills

(Posted 2014) [#2]

Methods are used with an instance of a class, whereas Functions are used with the class itself.

http://www.monkeycoder.co.nz/docs/html/Programming_Language%20reference.html#functions

http://www.monkeycoder.co.nz/docs/html/Programming_Language%20reference.html#methods

"Self" is a reference to the current object, the object which method is currently being called.

Heres a simple example:

Class Foo
  Field x:Float

  ' constructor
  Method New(x:Float)
    Self.x = x
  End

  Method GetX:Float()
    Return Self.x
  End

  Method SetX:Void(x:Float)
    Self.x = x
  End

  Function CreateFoo:Foo(x:Float)
    Local f:Foo = New Foo(x)
    Return f
  End
End

Function Main:Int()
  Local f:Foo = New Foo(10)
  Local tmpX:Float = f.GetX()
  Local newFoo:Foo = Foo.CreateFoo(20)
  Return True
End

Goodlookinguy

(Posted 2014) [#3]

I do believe invaderJim's tutorials go over this: http://www.monkeycoder.co.nz/Community/posts.php?topic=3318&page=1 | From the index anyways, it looks like it'll explain this.

dawlane

(Posted 2014) [#4]

This http://stackoverflow.com/a/155655 is possibly the best explanation of the difference between a function and a method.
As therevills says,

"Self" is a reference to the current object, the object which method is currently being called

Think of Self as special variable in an objects instance to it's own location in memory. NOTE: if you tried to use Self within the CreateFoo function, it will not compile and give you the error, "illegal use of Self within static scope" even though CreateFoo is within the class Foo, it is not part of an object instance. You could have had Function CreateFoo out side of the class, but I wouldn't recommend it for creating object instances. Functions outside of a class to me should be general purpose. Like wise you should never pass Self as a parameter to a function or method within a constructor (Method New()) as the object wouldn't exist until after then constructor has exited; it will just crash with an access violation.

dubbsta

(Posted 2014) [#5]

appreciate the help guys, you all get a star! :)~

Gerry Quinn

(Posted 2014) [#6]

The basic idea of object orientation is that you have an object (a chunk of data) combined with a collection of operations that work on the data. A method is such an operation which is automatically bound to a single instance of its class.

Consider the following example:

Class Rectangle
	Field width:Float
	Field height:Float
	
	Method GetArea:Float()
		Return width * height
	End
End

Function GetArea:Float( rect:Rectangle )
	Return rect.width * rect.height
End

The GetArea() method and function are functionally the same. But the method doesn't need to be told which rectangle to use (or at least it is told in a different way), and also it is nicely tidied away within the class scope.

At the lowest level of compiled code, both method and function will probably wind up exactly the same.