[Solved] ForEach loop with Maps

[BarryG]

I'm still getting used to maps, so the code below doesn't make sense to me. If I set the value of "icon" to 1, then ForEach/Next goes into an endless loop, but NOT if I set "icon" to 2 or 3. Why? What's so special about "1" that it doesn't stop the loop?

Reason for asking: I have a Map of all icons loaded by my app, but sometimes I'll load an icon on demand that ISN'T in the map (like "three=" below). So I need a way to work out if any given icon is in the map or not. I thought ForEach/Next could do this, but with an endless loop I can't use it.

Code: Select all

NewMap IconMap()

IconMap("1")=1
IconMap("2")=2
three=LoadIcon_(0,#IDI_APPLICATION) ; Purposely not in the map.

icon=1 ; Endless loop, but NOT if set to 2 or 3. Why?

ForEach IconMap()
  Debug IconMap(Str(icon))
Next

[DarkDragon]

By accessing a different key you change the current element. Store the old current element and restore it afterwards with PushMapPosition(Map()) and PopMapPosition(Map()):

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ForEach IconMap()
  PushMapPosition(IconMap())
  Debug IconMap(Str(icon))
  PopMapPosition(IconMap())
Next

However checking whether a key is inside a map is done via FindMapElement(Map(), Key$), you don't iterate all elements.

[BarryG]

Thanks, that helped me work out my problem! This was my goal:

Code: Select all

NewMap IconMap()

IconMap("1")=1
IconMap("2")=2
three=LoadIcon_(0,#IDI_APPLICATION) ; Purposely not in the map.

Debug FindMapElement(IconMap(),Str(1)) ; Non-zero means in the map.
Debug FindMapElement(IconMap(),Str(2)) ; Non-zero means in the map.
Debug FindMapElement(IconMap(),Str(three)) ; 0 means NOT in the map.

[Bisonte]

Code: Select all

Procedure.i IsInIconMap(Number)
  
  Protected Result = #False
  
  PushMapPosition(IconMap())
  
  If FindMapElement(IconMap(), Str(Number))
    Result = #True
  EndIf
  
  PopMapPosition(IconMap())
  
  ProcedureReturn Result
  
EndProcedure

Where IconMap() is global....

else

Code: Select all

Procedure.i IsInIconMap(Map IconMap(), Number)

[BarryG]

Thank you, Bisonte.

[boddhi]

Hello,

For further information (just in case),
We need to be careful, as some operations can implicitly create an element without an assignment:

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NewMap IconMap()

IconMap("1")=1
IconMap("2")=2

Debug FindMapElement(IconMap(),"3")

If IconMap("3"):EndIf

Debug FindMapElement(IconMap(),"3")

 
ALWAYS use FindMapElement() to check if a key really exists.

[Mesa]

It's a bug, you should inform fred on the appropriate forum.

M.

[mk-soft]

It's a bug, you should inform fred on the appropriate forum.

M.

The behaviour was changed in this point because it led to other problems in other points.
FindMapElement must be used explicitly.

[boddhi]

FindMapElement must be used explicitly.

As it's not explicitly explained in the (French, anyway) documentation, knowing this would have saved me, some time ago, the trouble of trying to understand why one of my codes wasn't working properly!

[AZJIO]

I always use AddMapElement() and have never encountered a problem yet. I think you are trying to shorten the entry using simplified assignment.

You list the map elements

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ForEach IconMap()
  Debug IconMap()
Next

When you set IconMap("1") in a loop, you probably reset the current position of the element listing, you have "1" every time, and always strive for "2".

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Dim Arr(2)

Arr(0) = 1
Arr(1) = 2
Arr(2) = 3

For i = 0 To 2
	Debug Arr(i)
Next

; Now guess why you always have the same number infinitely
For i = 0 To 2
	i=1
	Debug Arr(i)
Next

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NewList IconList()
AddElement(IconList())
IconList() = 1
AddElement(IconList())
IconList() = 2

ForEach IconList()
	Debug IconList()
Next

; Now guess why you always have the same number infinitely
ForEach IconList()
	SelectElement(IconList() , 0)
	Debug IconList()
Next