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Problem with EachIn?

Monkey Forums/Monkey Programming/Problem with EachIn?

AdamRedwoods(Posted 2011) [#1]
It may be just my opinion, but I don't think EachIn should be erroring out when trying to access a null (undefined?) object in an array.


Example:

Class CNode
	Field x:Int, y:Int
	
	Function Create:CNode[](n:Int[])
		Local nd:CNode[n.Length+1] ''too big of an array
		 
		Local i:Int =0
		For Local j:Int = 0 To n.Length-2 Step 2
			nd[i] = New CNode	
			nd[i].x = n[j+0]
			nd[i].y = n[j+1]
			i +=1

		Next
		Return nd
	End
End

Function Main()

	Local node:CNode[] = CNode.Create([5,1,5,6,8,6,4,4])
	
	For Local j:CNode = Eachin node
		Print "node:" +j.x+" "+j.y
	Next
End


Or is this proper behavior?


invaderJim(Posted 2011) [#2]
I think it's throwing the error when you try to access the x and y properties of the null object. If you comment out the Print statement, it rolls through the CNode array just fine.


Soap(Posted 2011) [#3]
Yeah, you just need to test if j is null or not before you print. But if it's actually the For loop that's crashing then that is indeed a bug.


AndyGFX(Posted 2011) [#4]
You have to always test if returned element is not null, but from my point of view, keyword Eachin is better using with List<T> or Map<K,V>

Here is my version of your code:


Class CNode
	Field x:Int, y:Int
	Field list:List<CNode>
	
	Method New()
		Self.list = New List<CNode>
	End Method
	
	Method Create:CNode(n:Int[])
		For Local j:Int = 0 To n.Length-2 Step 2
			Local nd:CNode = New CNode()
			nd.x = n[j+0]
			nd.y = n[j+1]
			Self.list.AddLast(nd)
		Next
	End
End

Function Main()

	Local node:CNode = New CNode()
	
	
	node.Create([5,1,5,6,8,6,4,4])
	
	For Local j:CNode = Eachin node.list
		Print "node:" +j.x+" "+j.y
	Next
End


or


Class CNode
	Field x:Int, y:Int
End
	
Function CreateNodeList:List<CNode>(n:Int[])
	Local list:List<CNode> = New List<CNode>
		For Local j:Int = 0 To n.Length-2 Step 2
			Local nd:CNode = New CNode()
			nd.x = n[j+0]
			nd.y = n[j+1]
			list.AddLast(nd)
		Next
	Return list
End

Function Main()

	Local node:List<CNode> = CreateNodeList([5,1,5,6,8,6,4,4])
	
	For Local j:CNode = Eachin node
		Print "node:" +j.x+" "+j.y
	Next
End



AdamRedwoods(Posted 2011) [#5]
Interesting, thanks for the responses.