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Difference Between New() and OnCreate()

Monkey Forums/Monkey Programming/Difference Between New() and OnCreate()

c.k.(Posted 2012) [#1]
Is there a difference? Obviously, there is... I can't do something like

[monkeycode]
x = New y("1")
[/monkeycode]

unless I have a New(s:String) method defined, even if I have an OnCreate(s:String) method defined.

If I never use parameters for creating new y objects, then I don't need New(), and OnCreate() triggers as well. I think.


therevills(Posted 2012) [#2]
Within your OnCreate method you would have to call "New" and return the object:

[monkeycode]x = y.OnCreate("1")
...

Class y
Field str:String

Function OnCreate:y(s:String)
local o:y = New y
o.str = s
Return o
End
End[/monkeycode]

With using the constructor ("new") you can replace most of that code:

[monkeycode]x = New y("1")
...

Class y
Field str:String

Method New(s:String)
self.str = s
End
End[/monkeycode]


ziggy(Posted 2012) [#3]
OnCreate is just a method on the App class. It's not called when a class is instantiated.


c.k.(Posted 2012) [#4]
Interesting. Thanks, guys.

Are there any general rules as to when to use New/OnCreate and when not to?


tiresius(Posted 2012) [#5]
Use OnCreate() callback for your application, use New() for instantiating your objects. Unless you want to wrap New() with OnCreate() for some reason ? I don't get it.


therevills(Posted 2012) [#6]
When I first read CK's post I thought he was talking about the "old" BlitzMax way to get around the lack of parameterised constructors... but now I am now so sure.

The "old" BlitzMax way was just to have a function (which I normally called "Create") to instante the object:

[bbcode]Type Sprite
Field x:Int
Field y:Int

Function Create:Sprite(x:Int, y:Int)
Local s:Sprite = New Sprite
s.x = x
s.y = y
Return s
End Function
End Type[/bbcode]


Gerry Quinn(Posted 2012) [#7]
There aren't any hard and fast rules about whether to initialise everything in New() or use an initialisation function (which might be called OnCreate() or Init() or whatever you want).

If you have multiple constructors many of which do similar things, an initialisation function for the common behaviours is useful.

As for why one doesn't overload New() for App-derived classes, I suspect the main reason Mark did it this way is to avoid people making mistakes by failing to call the super class constructor at the start of their own constructor. If there is some time-dependent initialisation needed on some targets this could also be allowed for.